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Compared with commercial lithium batteries with liquid electrolytes, all‐solid‐state lithium batteries (ASSLBs) possess the advantages of higher safety, better electrochemical stability, higher energy density, and longer cycle life; therefore, ASSLBs have been identified as promising candidates for next‐generation safe and stable high‐energy‐storage devices. The design and fabrication of solid‐state electrolytes (SSEs) are vital for the future commercialization of ASSLBs. Among various SSEs, solid polymer composite electrolytes (SPCEs) consisting of inorganic nanofillers and polymer matrix have shown great application prospects in the practice of ASSLBs. The incorporation of inorganic nanofillers into the polymer matrix has been considered as a crucial method to achieve high ionic conductivity for SPCE. In this review, the mechanisms of Li+ transport variation caused by incorporating inorganic nanofillers into the polymer matrix are discussed in detail. On the basis of the recent progress, the respective contributions of polymer chains, passive ceramic nanofillers, and active ceramic nanofillers in affecting the Li+ transport process of SPCE are reviewed systematically. The inherent relationship between the morphological characteristics of inorganic nanofillers and the ionic conductivity of the resultant SPCE is discussed. Finally, the challenges and future perspectives for developing high‐performance SPCE are put forward. This review aims to provide possible strategies for the further improvement of ionic conductivity in inorganic nanoscale filler‐reinforced SPCE and highlight their inspiration for future research directions.

Mn-based layered oxides are very attractive as cathodes for potassium-ion batteries (PIBs) due to their low-cost and environmentally friendly precursors. Their transfer to practical application, however, is inhibited by some issues including consecutive phase transitions, sluggish K+ deintercalation/intercalation, and serious capacity loss. Herein, Mg-Ni co-substituted K1/2Mn5/6Mg1/12Ni1/12O2 is designed as a promising cathode material for PIBs, with suppressed phase transitions that occurred in K1/2MnO2 and improved K+ storage performance. Part of Mg2+ and Ni2+ occupies the K+ layer, playing the role of a "nailed pillar", which restrains metal oxide layer gliding during the K+ (de)intercalation. The "Mg-Ni pinning effect" not only suppresses the phase transitions but also reduces the cell volume variation, leading to the improved cycle performance. Moreover, K1/2Mn5/6Mg1/12Ni1/12O2 has low activation barrier energy for K+ diffusion and high electron conductivity as demonstrated by first-principles calculations, resulting in better rate capability. In addition, K1/2Mn5/6Mg1/12Ni1/12O2 also delivers a higher reversible capacity owing to the participation of the Ni element in electrochemical reactions and the pseudocapacitive contribution. This study provides a basic understanding of structural evolution in layered Mn-based oxides and broadens the strategic design of cathode materials for PIBs.

O3-type NaCrO2 is attracting increasing attention as potential cathode material for sodium-ion batteries (SIBs). Bare NaCrO2 is usually synthesized by a solid-state reaction and suffers from serious capacity decay and poor power capability. Modification by coating is an effective method to improve the electrochemical properties, but it inevitably reduces the energy density. To avoid the decrease of energy density and optimize the electrochemical performance, a specific route, i.e., a freeze-drying-assisted sol-gel method, has been adopted to synthesize bare NaCrO2 in this work. Three-phase coexistence during charging is confirmed for the first time, which contributes to delaying the disappearance of the O3 phase and then improving the structural reversibility, resulting in superior cycle stability (∼50% capacity retention after 3000 cycles at 5C). Meanwhile, as-synthesized NaCrO2 delivers an outstanding rate capability (82.1 mAh g-1 at 50C), which is attributed to the fast Na+ diffusivity and high electronic conductivity proved by density functional theory (DFT) calculations. It is worth mentioning that NaCrO2 also exhibits excellent electrochemical properties when used as a cathode for potassium-ion batteries (PIBs). This work provides new perspectives on the structural evolution of NaCrO2, and the results are expected to contribute to the development of SIBs and PIBs.

Practical application of lithium metal anodes in high-energy rechargeable batteries is impeded by the issue of Li dendrite growth. Herein, an exceptional hydrophobic MAF-6 material is utilized to modify polypropylene (PP) separator to yield a superorganophilic MAF-6/PP composite separator. Owing to a combination of superorganophilicity with three-dimensional ordered porosity, the MAF-6/PP achieves a Li ion transference number of 0.78. Homogeneous and dense Li plating behaviors are present in cells with MAF-6/PP which can afford uniform Li ion flux. The MAF-6/PP enables Li|Cu cells to run steadily for over 350 cycles at 0.5 mA cm−2-1 mAh cm−2 with an average coulombic efficiency (CE) of 98.8%, symmetric Li|Li cells to work stably for 2200 h without short-circuit at 0.5 mA cm−2-1 mAh cm−2, and Li|LiFePO4 cells to retain a reversible capacity of 102.4 mAh g−1 after 1500 cycles at 1C with a capacity retention of 73.2% and a CE of 99.9%.

All-solid-state lithium batteries (ASSLB) are promising candidates for next-generation energy storage devices. Nevertheless, the large-scale commercial application of high energy density ASSLB with the polymer electrolyte still faces challenges. In this study, a thin solid polymer composite electrolyte (SPCE) is prepared through a facile and cost-effective strategy with an infiltration of thermoplastic polyurethane (TPU), lithium salt (LiTFSI or LiFSI), and halloysite nanotubes (HNTs) in a porous framework of polyethylene separator (PE) (TPU–HNTs–LiTFSI–PE or TPU–HNTs–LiFSI–PE). The composition, electrochemical performance, and especially the effect of anions (TFSI− and FSI−) on cycling performance are investigated. The results reveal that the flexible TPU–HNTs–LiTFSI–PE and TPU–HNTs–LiFSI–PE with a thickness of 34 μm exhibit wide electrochemical windows of 4.9 and 5.1 V (vs. Li+/Li) at 60 ℃, respectively. Reduction in FSI− tends to form more LiF and sulfur compounds at the interface between TPU–HNTs–LiFSI–PE and Li metal anode, thus enhancing the interfacial stability. As a result, cell composed of TPU–HNTs–LiFSI–PE exhibits a smaller increase in interfacial resistance of solid electrolyte interphase (SEI) with a distinct decrease in charge-transfer resistance during cycling. Li|Li symmetric cell with TPU–HNTs–LiFSI–PE could keep its stable overpotential profile for nearly 1300 h with a low hysteresis of approximately 39 mV at a current density of 0.1 mA cm−2, while a sudden voltage rise with internal cell impedance-surge signals was observed within 600 h for cell composed of TPU–HNTs–LiTFSI–PE. The initial capacities of NCM|TPU–HNTs–LiTFSI–PE|Li and NCM|TPU–HNTs–LiFSI–PE|Li cells were 149 and 114 mAh g−1, with capacity retention rates of 83.52% and 89.99% after 300 cycles at 0.5 C, respectively. This study provides a valuable guideline for designing flexible SPCE, which shows great application prospect in the practice of ASSLB.

Designing a novel anode material with suitable elemental composition and bonding structure for improving the limited capacity and poor lithium-ion conductivity of lithium-ion batteries (LIBs) is still challenging. Here, guided by first-principles calculations, we report a higher crystal symmetric, cation-disordered zinc blende Zn0.5Ge0.5P anode material with high-capacity and high-rate capability owing to superior electron and lithium-ion transport compared to the parent allotrope chalcopyrite ZnGeP2. The Zn0.5Ge0.5P anode exhibits a large specific capacity of 1435 mA h g−1 with a high initial Coulombic efficiency of 92%. An amorphization–conversion–alloying reaction mechanism is proposed based on ex situ characterizations including X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. During lithiation, the material phase-changes through Li3P, LiZnGe, β-Li2ZnGe, and α-Li2ZnGe intermediates that provide suitable transport channels for fast diffusion of lithium ions. During delithiation, LiZn, Li15Ge4, and Li3P nanoparticles reassemble into Zn0.5Ge0.5P. A Zn0.5Ge0.5P–TiC–C composite with finer particle size and enhanced electronic conductivity exhibits an initial specific capacity of 1076 mA h g−1 and a capacity retention of 92.6% after 500 cycles.

Anatase TiO2 is considered as a promising anode material for sodium-ion batteries, but the inherent semiconductor properties and the sluggish Na+ diffusion kinetics limit its further development. To overcome these inherent drawbacks, heterojunction TiO2@TiOF2 constructed with two-dimensional nanosheets is prepared by the hydrothermal method. When heterojunction TiO2@TiOF2 is used as a sodium ion battery material, a stable cycling performance of up to 10 000 cycles can be achieved at a high current density of 5000 mA g−1, probably due to the heterojunction structure, the exposed (0 0 1) facet of TiO2 and the in situ formed NaF protective layer. Density functional theory (DFT) calculations further reveal that the heterostructure TiO2@TiOF2 nanosheets possess better electrical conductivity and lower formation energies of Na+ ions than those of the separated TiO2 and TiOF2. This work offers a new strategy to design novel heterojunction structures for the electrochemical sodium storage.

Mn-based layered oxides, as potential cathodes for potassium-ion batteries (PIBs), face major challenges such as consecutive phase transition, serious capacity loss, and sluggish K+ transport kinetics. Herein, Co–Mg co-substituted K0.45Co1/12Mg1/12Mn5/6O2 is designed as a promising cathode material for PIBs to conquer the above issues in this work. Co3+–Mg2+ ions occupying the Mn3+ sites are confirmed to effectively alleviate the Jahn–Teller distortion induced by Mn3+ ions. P3-K0.45Co1/12Mg1/12Mn5/6O2 exhibits highly reversible single-phase structural evolution during the K+ deintercalation/intercalation. In contrast, the pristine K0.45MnO2 electrode experiences incompletely reversible structural variation from a P′3 to P3 phase. The increase of structural stability in the Co–Mg co-substituted sample is the main reason leading to improved cycling stability. Moreover, K0.45Co1/12Mg1/12Mn5/6O2 delivers better rate capability resulting from faster K+ diffusion compared to K0.45MnO2. Therefore, Co–Mg co-substitution is an effective strategy to enhance the structural stability and electrochemical properties of Mn-based layered oxides in PIBs.

Zinc-air battery is one of the most promising next-generation energy conversion and storage systems. Green and low-cost catalysts with high oxygen reduction reaction (ORR) catalytic activity are desired to meet the requirements of Zinc-air batteries. Herein, poly-active centric Co3O4-CeO2/Co-N-C (ketjenblack carbon) catalysts were prepared by a facile method. The Co3O4 and CeO2 nanoparticles are uniformly anchored on the surface of Co and N doped carbon support. The half-wave potential of Co3O4-CeO2/Co-N-C in the rotating disk electrode testing is close to that of Pt/C. The Zn-air battery using Co3O4-CeO2/Co-N-C as the cathode catalyst can provide a high specific capacity of 728 mA h g−1 at 20 mA cm−2 and maintain a stable discharge voltage. The remarkable catalytic performance is mainly attributed to the synergistic effect among Co3O4, CeO2 and Co-N-C, the outstanding electrical conductivity and the large surface area. Benefitting from the high catalytic activity, environmental friendliness and the facile synthesis process, Co3O4-CeO2/Co-N-C catalyst lends itself well to a great prospect in the application of metal-air batteries.

Construction of three-dimensional (3D) composite lithium metal anodes (LMAs) based on Li melt-infusion into a 3D porous scaffold has been demonstrated to be effective for solving the issue of the considerable relative volume change of LMAs during Li plating/stripping. However, little attention has been paid to controllable regulation of the structure and interface of 3D composite LMAs. In this study, 3D composite LMAs, namely Li–AuLi3@CF electrodes, are firstly fabricated by infusion of molten Li into carbon fiber (CF) paper modified with nanoporous gold (NPG) which is converted to AuLi3 after infusion. We herein demonstrate a synergistic structure and interface engineering strategy realized by a simple and effective pre-stripping protocol to initially expose a portion of the 3D AuLi3@CF scaffold to create “PS-Li-AuLi3@CF” electrodes, which greatly boosted the electrochemical performance. Symmetrical Li|Li cells with PS-Li-AuLi3@CF electrodes show an overpotential of 111 ​mV after cycling at a current density of 0.5 ​mA ​cm−2 for 1800 ​h. Additionally, Li|LiFePO4 (LFP) and Li|sulfurized polyacrylonitrile (SPAN) full cells with PS-Li-AuLi3@CF electrodes exhibit a high capacity retention of 96.1% with a Coulombic efficiency (CE) of 99.2% after 1000 cycles at 5C, and a capacity retention of 70.6% with a CE of 99.8% after 1000 cycles at 2C, respectively. This work provides a simple and highly effective method for engineering the structure and interface of 3D composite LMAs to boost their electrochemical performance for high-energy-density rechargeable lithium metal batteries (LMBs).

Alloy anode with good reversibility of lithium plating/stripping and long cycling stability is considered as promising anode materials. Here, Cu–Sn alloy is used as the substrate for Li deposition to induce the most densely packed arrangement of Li atoms, thus presenting high lithiophilicity and improving Li plating behaviors. The LiFePO4-based full cell with the as-prepared dendrite-free Li metal anode retained at 85 mAh g−1 with a high coulombic efficiency of 99.5% after 300 cycles, presenting a capacity retention of 79.4%. This strategy provides a new perspective to structure dendrite-free Li anode for the next-generation high-energy density batteries.

As one of the most promising next-generation safe and green energy storage technologies, aqueous Zn-ion batteries have attracted considerable attention in recent years. However, their working mechanism is still controversial. Also, their performance needs to be further improved to meet the requirement of widespread applications. Herein, we developed a nanoflower-like MnO2/C composite with two-electron reaction pathway for use as a cathode material in aqueous Zn-ion batteries. Benefiting from the large specific surface area of the nanoflower-like structure, high conductivity of the carbon materials and the low crystallinity of birnessite-type MnO2, the Zn-ion battery using MnO2/C as the cathode material could carry out a deep and fast reaction via the Mn4+/Mn2+ two-electron pathway. At 300 mA g−1, the battery could retain a high specific capacity of 279.7 mA h g−1 after 300 cycles. The second electronic reaction process of Mn3+/Mn2+ could also work at a high current density. A high initial discharge capacity of more than 200 mA h g−1 was achieved at a high current density of 2000 mA g−1. A two-electron working mechanism of the layered-MnO2 cathode material is proposed. Due to the advantages of high capacity, high rate performance and good stability, the MnO2/C composite is a promising cathode material for aqueous Zn-ion batteries, which holds potential for applications in electric vehicles and grid energy storage.

Composite solid-state electrolytes (CSEs) that integrate the merits of different components are considered to be promising candidates for next-generation high-energy density lithium metal batteries. Herein, we have successfully designed a flexible CSE membrane consisting of the ceramic conducting Li1.3Al0.3Ti1.7(PO4)3 (LATP) filler, polyethylene oxide (PEO) matrix, and 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (BMP-TFSI) ionic liquid. In particular, the addition of ionic liquid (BMP-TFSI) can not only decrease the interface impedance between the polymer and LATP ceramic fillers and improve the ionic conductivity, but also prevent the adverse reaction between Ti4+ in LATP and Li metal and further enhance the interface stability. Benefitting from the synergistic effect of organic–inorganic hybrids, the obtained composite electrolyte membrane achieves an excellent ionic conductivity of 2.42 × 10−4 S cm−1 at 30 °C and a wide electrochemical stability window of 5 V (vs. Li+/Li). Moreover, the CSE membrane exhibits outstanding Li dendrite suppression capability, which is proved by galvanostatic Li plating/stripping tests for 1000 h. Assembled with this solid electrolyte membrane and a commercial LiFePO4 cathode, all-solid-state lithium metal batteries demonstrate superior rate capability and outstanding cycling stability at both 30 and 45 °C. These results demonstrate that such a flexible composite electrolyte is a promising alternative electrolyte for practical high-energy density all-solid-state batteries.

The construction of a lithiophilic phase on the surface of a current collector with a lithiophobic nature is an effective method to suppress Li dendrite growth by reducing the overpotential for Li nucleation and inducing the growth of homogeneous Li nuclei to obtain high-performance lithium metal anodes (LMAs). Nevertheless, the structural regulation of the lithiophilic phase and the underlying mechanism of lithiophilicity have been overlooked in previous studies. In this study, we designed a triporous, nanoporous AuLi3 (NPAuLi3) nanosheet-modified Ni foam (NF) (NPAuLi3@NF) composite current collector for use in LMAs. First principle calculations revealed that the lithiophilicity of the AuLi3 phase originates from the strong electronic interaction between the Au and Li atoms. The morphological characterization demonstrated that the as-designed NPAuLi3@NF current collector not only guided homogeneous Li nucleation and growth during the Li plating process, but also induced uniform Li removal during the Li stripping process, which effectively suppressed Li dendrite growth and formation of dead Li, leading to a boosted electrochemical performance in LMAs. The symmetric Li|Li cells with the NPAuLi3@NF-based LMAs could run stably for 1990 and 1420 h without cell failure at current densities of 1 and 2 mA cm−2 with a capacity of 2 mA h cm−2, respectively, and the Li@NPAuLi3@NF|LFP full cells showed an excellent capacity retention of 83.8% with a coulombic efficiency of 99.8% at 5C after 1000 cycles, and a good rate capability. This work provides insight into the design of the composition and structure of the lithiophilic phase on the surface of the current collector skeleton to obtain high-performance LMAs.

The NiS2 nanosheet array on Ni foil (NiS2/NF) was prepared using an in situ growth strategy and sulfidation method and was used as the cathode of lithium sulfur battery. The unique nanostructure of the NiS2 nanosheet array can provide abundant active sites for the adsorption and chemical action of polysulfides. Compared with the sulfur powder coated pure NF (pure NF-S) for lithium sulfur battery, the sulfur powder coated NiS2/NF (NiS2/NF-S) electrode exhibits superior electrochemical performance. Specifically, the NiS2/NF-S delivered a high reversible capacity of 1007.5 mAh g−1 at a current density of 0.1 C (1 C= 1675 mA g−1) and kept 74.5% of the initial capacity at 1.0 C after 200 cycles, indicating the great promise of NiS2/NF-S as the cathode of lithium sulfur battery. In addition, the NiS2/NF-S electrode also showed satisfactory electrochemical performance when used as the cathode for sodium sulfur battery.

Cu2P7-black P-MWCNT (CuP5/MWCNT) is prepared by a facile mechanical milling method. When used as anodes for Li/Na-ion batteries, the composite delivers high comprehensive performances: initial Coulombic efficiency up to 90/84%, 1455/1170 mA h g−1 after 200 cycles, and 960/580 mA h g−1 at 5 A g−1 for Li/Na-ion batteries, respectively. The performances can be attributed to the hybridized strategy of two-dimension layered structure of Cu2P7, black P, and one-dimension multiwall carbon nanotubes. The former offers a fast transport channel for Li/Na-ions and the latter provides for fast transport of electrons and accommodates the volume variation during cycling. In addition, the synergistic effect among different phases also leads to enhanced performance. The integrated strategy of one-dimensional and two-dimensional advantages can excite more research interest in the energy-storage field.

The metal-air battery is a form of renewable energy generation technology that produces energy electrochemically and can address energy concerns in the near future. However, state-of-the-art Pt electrocatalysts often suffer from agglomeration or detachment from carbon supports under prolonged operation, eventually limiting the long-term utilization of metal-air batteries. In this work, Pt nanoparticles were deposited on sulfur-doped nanocarbon to increase its stability. We first synthesized sulfur-doped (S-doped) and pristine carbon as support materials via a plasma process, and thereafter loaded platinum (Pt) nanoparticles onto the S-doped and pristine carbon matrix. From a sintering test at 600 °C, the Pt nanoparticles supported on pristine carbon increased from 2.4 to 5.2 nm; meanwhile, the average size of Pt NPs supported on S-doped carbon only increased from 2.2 to 2.51 nm. From the electrochemical analyses, the mass activity of Pt on pristine and S-doped carbon supports decreased by 25% and 10%, respectively, after 1500 cycles. The results proposed that the sulfide C–S–C bond provided a strong platinum-S-doped carbon support interaction between the support materials and the loaded Pt nanoparticles. Thus, S-doped carbon supports can serve as a stabilizer of Pt nanoparticles to enhance their durability in the application of metal-air batteries and other electrochemical devices.

Transition metal sulfides such as Ni–Co sulfides are promising electrode materials for supercapacitors owing to their advantageous electrical conductivity. Current approaches for the synthesis of Ni–Co sulfides normally involve wet chemical sulfurization. In this work, we demonstrate a facile method for synthesizing CoxNi1-xS2 (0

Phosphides are promising anode candidates profiting from their relatively smaller voltage hysteresis which thus are promising to be high energy efficiency and power capabilities for secondary batteries, compared with the corresponding fluorides, oxides and sulfides. Herein we for the first time synthesized ternary Cu 2 P 7 /CuP 2 /graphite composite by a facile ball milling method. When initiated as anodes for Li-ion batteries, the as-synthesized ternary composite provides 1415 mA h g −1 after 100 cycles and 684 mA h g −1 at a high current density of 10 A g −1 . When initiated as anodes for Na-ion batteries, the as-synthesized ternary composite provides 1254 mA h g −1 after 100 cycles and 200 mA h g −1 at a high current density of 5 A g −1 . These electrochemical performances are comparable or even surpass the P/C, CuP 2 /C and other transition metal phosphides reported before. The enhanced performances can be attributed to the high P concentration, layered structure and small band gap of the Cu 2 P 7 phase and the heterointerface between these phases, which not only assists electron and Li-ion transportation and but also creates more active sites endowed by interfacial coupling and positive electrochemical synergistic effect. The multiphase design strategy can further excite more research interest in the energy-storage field.

Various P-Ge compounds including GeP5 and GeP3 can be easily synthesized by a direct ball milling method while GeP can not. Herein, we successfully synthesize binary-phase Ge2P3 composite which derived from layered GeP and black P. When applied as anodes for Li-ion batteries, the as-synthesized binary-phase composite delivers a large reversible capacity of 1605 mA h g−1 with a high initial Coulombic efficiency of 89%, retains 1380 mA h g−1 after 100 cycles and even achieves 920 mA h g−1 at a current density of at 5 A g−1. Also, for sodium-storage it shows a reversible capacity of 970 mA h g−1 with an initial Coulombic efficiency of 88% and retains 890 mA h g−1 after 100 cycles. The performance can be attributed to the following merits: the binary Li/Na-storage components host more Li/Na ions, the layered structure favors Li/Na-ion transportation and the abundant heterointerfaces increase the amount of active sites.

This work presents a desirable bifunctional catalyst—Co3O4 nanoparticles anchored on nitrogen-doped partially exfoliated multiwall carbon nanotubes (Co3O4/N-p-MCNTs)—for oxygen reduction reaction (...

Recently, rechargeable Zn-ion batteries (ZIBs) have attracted incremental attention as prospective energy storage devices for grid-scale applications and flexible devices, due to their low cost, environmental benignity, high safety and unique properties of the Zn metal. However, the sustained development of high-performance ZIBs is hindered by the limited availability of cathode materials. Here, for the first time, we demonstrate MoS2 with expanded inter-layer spacing (E-MoS2) can be a promising cathode candidate for rechargeable and flexible ZIBs. By X-ray diffraction (XRD) and Raman studies, a reversible Zn2+ ion intercalation/deintercalation mechanism was revealed. The E-MoS2 electrode delivers a specific capacity of 202.6 mA h g−1 at 0.1 A g−1, a desirable energy density of 148.2 Wh kg−1 and good cycle stability with a capacity retention ratio of 98.6% over 600 cycles. By using the newly-developed starch/ polyacrylamide (PAM) based polymer electrolyte with high zinc ion conductivity, a quasi-solid Zn/E-MoS2 battery was developed, which exhibits decent electrochemical performance even under various heavy deformations, holding great potential for applications in future flexible and wearable devices.

In this work, a unique artificial interface combing characteristics of both high ionic and electronic conductivities has been successfully constructed at the surface of Ni-rich LiNi0·8Co0·1Mn0·1O2 (NCM811). The ionic conductor layer is fabricated through reacting H3PO4 with the lithium residuals on the surface of NCM811 to form Li3PO4. The interface with high electronic conductivity is constructed by attaching graphene fragments to the NCM811 spherical particles. Due to the synergistic effect of the Li3PO4 coating layer and the graphene network, the modified sample (GN-LPO-NCM811) exhibits high capacity retention of 94.3% after 150 cycles at 0.5C between 3.0 and 4.3 V, while the pristine material shows a much lower retention of only 88.1%. In addition, the GN-LPO-NCM811 also presents improved cycling stability at elevated temperature of 55 °C. Even at an extremely high rate of 10C, the GN-LPO-NCM811 still remains 70% of its original capacity, while the pristine NCM811 only delivers 50% of the capacity. The stable cycling performance of GN-LPO-NCM811 is demonstrated in a full cell with graphite anode at ambient temperatures. Importantly, the thermal stability of the modified samples is also greatly enhanced. This study provides an effective method to improve the electrochemical performance of LiNi0·8Co0·1Mn0·1O2.

Highlights Single-atom M-N4/N-doped carbons (M = Fe, Co) prepared as OER/ORR catalysts.Ultrasonication-assisted plasma engineering used for catalyst synthesis.Co-N4/NC outperformed benchmark commercial catalysts in practical Zn–air battery test.DFT calculations provided insights into the origin of superior ORR/OER performance. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-020-00581-4, As bifunctional oxygen evolution/reduction electrocatalysts, transition-metal-based single-atom-doped nitrogen–carbon (NC) matrices are promising successors of the corresponding noble-metal-based catalysts, offering the advantages of ultrahigh atom utilization efficiency and surface active energy. However, the fabrication of such matrices (e.g., well-dispersed single-atom-doped M-N4/NCs) often requires numerous steps and tedious processes. Herein, ultrasonic plasma engineering allows direct carbonization in a precursor solution containing metal phthalocyanine and aniline. When combining with the dispersion effect of ultrasonic waves, we successfully fabricated uniform single-atom M-N4 (M = Fe, Co) carbon catalysts with a production rate as high as 10 mg min−1. The Co-N4/NC presented a bifunctional potential drop of ΔE = 0.79 V, outperforming the benchmark Pt/C-Ru/C catalyst (ΔE = 0.88 V) at the same catalyst loading. Theoretical calculations revealed that Co-N4 was the major active site with superior O2 adsorption–desorption mechanisms. In a practical Zn–air battery test, the air electrode coated with Co-N4/NC exhibited a specific capacity (762.8 mAh g−1) and power density (101.62 mW cm−2), exceeding those of Pt/C-Ru/C (700.8 mAh g−1 and 89.16 mW cm−2, respectively) at the same catalyst loading. Moreover, for Co-N4/NC, the potential difference increased from 1.16 to 1.47 V after 100 charge–discharge cycles. The proposed innovative and scalable strategy was concluded to be well suited for the fabrication of single-atom-doped carbons as promising bifunctional oxygen evolution/reduction electrocatalysts for metal–air batteries. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-020-00581-4

Ni-rich layered oxide (LiNi0.8Co0.1Mn0.1O2) has become popular commercial cathode material for lithium ion batteries, due to its high working potential and high specific capacity. It is still a challenge, however, to maintain the structure and performance under extreme conditions, such as at high charging cutoff (≥4.5 V), high temperature (≥60 °C) and higher charge-discharge rate (≥3 C). Herein, Poly (pyrrole-co-citral nitrile) (PPC) optimized interfacial layer is designed and constructed on the surface of LiNi0.8Co0.1Mn0.1O2 by an in situ photopolymerization self-assembly technology. The sweater-like co-polymer coating provides an integral protection from side reaction, particle rupture and irreversible phase transition during cycling under the extreme conditions. Furthermore, the delocalized π bonds and cross-linked network structure of the co-polymer coating ensure the efficient and stable interface between electrolyte and electrode. This work offers a novel and useful strategy to enhance the electrochemical performance of Ni-rich cathode materials for high-energy lithium ion batteries at extreme conditions.

Lithium–sulfur battery with high theoretical capacity becomes the subject of recent attention. Its commercial progress is impeded by its poor electrical conductivity and high dissolubility of intermediate products in organic electrolyte. In the present work, we report a novel three-dimensional graphene-wrapped porous carbon (3D-G) to accommodate sulfur, which consists of outside highly stable interconnected graphene-like sheets and inner activated porous carbon. The 3D-G was synthesized from cheap polyacrylic acid cation-exchange resin, which introduces nickel ions as catalysts in the carbonization process, as a cost effective, facile and simple method. This 3D-G showed hierarchical pores: 0.7 nm micropores and macropores, providing a large specific surface area of 1375.08 m2 g−1. Benefiting from this unique structure, the 3D-G performed well as host materials to achieve a high sulfur content (75.4 wt%). Such a 3D-G@S composite exhibits capacity-fading rate as low as 0.28% per cycle over 100 cycles at 0.1 C, and good cyclability at various cycling rates (0.1–1 C).

Rechargeable lithium oxygen batteries (LOBs) are one of the most promising energy storage systems by virtue of their high energy density and environmental amiability. However, the development of LOBs is still hindered by some critical issues. Herein, 3D hexapod-shaped Co-ZIFs-thiourea/dimethyl sulfoxide (H-Co-ZIFs-S) derived Co nanoparticles embedded into nitrogen and sulfur co-doped carbon (H-Co-NSC) are developed, and then low content of ruthenium nanoparticles are decorated on the surface to obtain Ru/H-Co-NSC as efficient catalyst for LOBs. The Ru/H-Co-NSC catalysts exhibits unique structure and catalytic properties, such as accommodating the insoluble discharge product Li2O2, promoting the transportation of ions/O2, enhancing the electronic conduction, demonstrating excellent OER/ORR kinetics as well. In addition, the Ru-decorated nanoparticles could effectively suppress some side-reactions caused by the exposed carbon of H-Co-NSC in LOBs. First-principles Density functional theory (DFT) calculations reveal the cooperative effect of multiple active sites in Ru/H-Co-NSC can effectively promote the ORR/OER kinetics in LOBs. Therefore, the LOBs with Ru/H-Co-NSC cathode provide a positive catalytic capacity with low overpotential, large specific capacities, long cycle life and superior reversibility. Our work may pave the way to design more advanced catalysts for metal-air batteries with superior electrochemical performance.

Constructing the M-N-C (M = Fe, Co, etc.) with meso- and macroporous structures is an effective strategy for designing the high-performance catalysts towards oxygen reduction reaction (ORR). However, these structures can hardly be achieved via the pyrolysis of classic metal-organic frameworks. Herein, we prepare the CoFe nanoparticles with surface oxides dispersed in Co/Fe-N-C support via carbonizing melamine and ethylenediaminetetraacetic acid chelated with metal ions. This hybrid exhibits high proportions of meso- and macropores along with excellent ORR catalytic activity, as evidenced by the half-wave potentials of 0.91 and 0.61 V (vs. RHE) in 0.1 M KOH and 3.5 wt% NaCl, respectively. The Al/Mg-air batteries with this catalyst exhibit superior performance to those employing Pt/C, primarily derived from the enlarged pore diameters and the exposed ORR active sites substantially enhancing the air-electrode performance. Our study provides an avenue to broaden the pore sizes of M-N-C for boosting its ORR catalytic activity.

Highly efficient and low-cost nonprecious metal electrocatalysts that favor a four-electron pathway for the oxygen reduction reaction (ORR) are essential for high-performance metal–air batteries. Herein, we show an ultrasonication-assisted synthesis method to prepare Mn3O4 quantum dots (QDs, ca. 2 nm) anchored on nitrogen-doped partially exfoliated multiwall carbon nanotubes (Mn3O4 QDs/N-p-MCNTs) as a high-performance ORR catalyst. The Mn3O4 QDs/N-p-MCNTs facilitated the four-electron pathway for the ORR and exhibited sufficient catalytic activity with an onset potential of 0.850 V (vs reversible hydrogen electrode), which is only 38 mV less positive than that of Pt/C (0.888 V). In addition, the Mn3O4 QDs/N-p-MCNTs demonstrated superior stability than Pt/C in alkaline solutions. Furthermore, a Zn–air battery using the Mn3O4 QDs/N-p-MCNTs cathode catalyst successfully generated a specific capacity of 745 mA h g–1 at 10 mA cm–2 without the loss of voltage after continuous discharging for 105 h. The superior...

LiNi0.5Mn1.5O4 is a promising cathode material for high power lithium ion batteries (LIBs) for electric vehicles (EVs) and hybrid electric vehicles (HEVs). For the first time we design a tri-functional coating to improve the cycling performance of LiNi0.5Mn1.5O4. With the designed BiPO4 coating, the capacity retentions of LiNi0.5Mn1.5O4 are largely improved from 84.3% to 93.6% at 0.5 C after 50 cycles and from 80.6% to 96.2% at 10 C after 100 cycles. The tri-functional coating reduces the charge transfer resistance of LiNi0.5Mn1.5O4 cathode and plays a critical role in enhancing the electrochemical performance and lifetime. This strategy provides a new way to modify electrode materials to elevate the performance of LIBs.

The increasing demand for portable electronic devices and hybrid electric vehicles stimulates the development of supercapacitors as an advanced energy storage system. Here, we demonstrate a binder-free nickel hydroxide@nanoporous gold/Ni foam (Ni(OH)2@NPG/Ni foam) electrode for high-performance supercapacitors, which is prepared by a facile three-step fabrication route including electrodeposition of Au-Sn alloy on Ni foam, chemical dealloying of Sn and electrodepostion of Ni(OH)2 on NPG/Ni foam. Such Ni(OH)2@ NPG/Ni foam electrode is composed of a thin layer of conformable Ni(OH)2 nanoflakes supported on three-dimensional (3D) hierarchically porous NPG/Ni foam substrate. The resulting Ni(OH)2@NPG/Ni foam electrode can offer highways for both electron transfer and ion transport and lead to an excellent electrochemical performance with an ultrahigh specific capacitance of 3,380 F g–1 at a current density of 2 A g–1. Even when the current density was increased to 50 A g–1, it still retained a high capacitance of 1,927 F g–1. The promising performance of the Ni(OH)2@NPG/Ni foam electrode is mainly ascribed to the 3D hierarchical porosity and the highly conductive network on the NPG/Ni foam composite current collector, as well as the conformal electrodeposition of Ni(OH)2 active material on the NPG/Ni foam, which induces the formation of interconnected porosity both on the top surface and on the inner surface of the electrode. This inspiring electrochemical performance would make the as-designed electrode material become one of the most promising candidates for future electrochemical energy storage systems.

Cathode materials LiMn 0.5 Fe 0.5 PO 4 /C and LiMnPO 4 /C were synthesized by a high-energy ball-milling assisted sol-gel method. The LiMn 0.5 Fe 0.5 PO 4 consists of nanorods and nanoparticles homogeneously wrapped with highly ordering carbon. The increased Neel-temperature and decreased effective magnetic moment of LiMn 0.5 Fe 0.5 PO 4 /C revealed the microstructure differences from LiMnPO 4 /C. Meanwhile, tiny amount of ferromagnetic impurities is detected in LiMn 0.5 Fe 0.5 PO 4 /C by magnetic tests. The synergetic effects of Fe substitution and carbon coating remarkably improve rate capacity and cyclic stability of LiMn 0.5 Fe 0.5 PO 4 /C. This solid solution delivers initial discharge capacities of 128.6 mAh g −1 and 116.3 mAh g −1 and capacity retentions of 93.5% and 90.3% after 100 cycles at 1C and 2C respectively, significantly better than LiMnPO 4 /C.

Lithium metal batteries (LMBs) have received extensive attention and research interest as high specific energy systems. However, the issues of Li dendrites growth in LMBs restrict their practical applications. The development of lithiophilic collectors can effectively solve the issues of Li dendrites growth. This study reports excellent lithium storage performance of lithiophilic nanosheet arrays which consist of electronic conductor Ni and ionic conductor Li2O (Ni-LONSs) on Ni foil (NF) fabricated via a simple preparation method for LMBs. The ionic conductor Li2O of the Ni-LONSs layer is lithiophilic and can induce uniform Li deposition on the Ni-LONSs collector. In addition, the nanosheet array structure of the Ni-LONSs collector is beneficial to slow down the volume change of the Li plating/stripping. In comparison with the NF collector, due to the specific nanosheet array structure of Ni-LONSs collector, the Ni-LONSs collector demonstrates excellent coulombic efficiency of 97.2% after 280 cycles (95.7% after 100 cycles of NF collector) and satisfactory cycling lifespan of 340 h (about 120 h of NF collector) at 0.5 mA cm-2with 1.0 mAh cm-2. Furthermore, the Ni-LONSs collector shows superior electrochemical performance in Ni-LONS/Li∣LiFePO4full cells. The excellent lithium storage performance of Ni-LONSs collector with mixed ionic/electronic conductor is conducive to the development and practical applications of LMBs.

Lithium–sulfur batteries with a high energy density are promising energy storage devices. The realization of lithium–sulfur batteries is mainly hindered by the dissolution of the intermediate polysulfides. In the present work, a new physical and chemical entrapment method of the polysulfides has been proposed, which used CMK-3 as the carbon scaffolds and a MnO 2 coating layer for chemisorption. Such a bi-functional framework provides efficient trapping for the polysulfides, achieving a reversible capacity of 600 mAh g −1 after 100 cycles at 0.1 C with a 73.4 wt% sulfur loading in the composite.

Using electrical vehicles instead of traditional ones is very important for reducing fossil oil consumption and carbon emissions. Spinel LiNi0.5Mn1.5O4 is considered as a promising cathode material for advanced lithium ion batteries owing to its high power density. Nevertheless, it suffers badly from the interfacial reactions with the electrolyte at high operation potential, which degrades its electrochemical performance. The strategy of the present study is to prevent direct contact between LiNi0.5Mn1.5O4 and the electrolyte by using a surface coating in order to reduce solid electrolyte interfacial reactions and consequently enhance its cycling performance. The experimental results indicated that as-prepared LiNi0.5Mn1.5O4 sintered at 900 °C possessed the highest initial specific capacity of 132.4 mA h·g−1 at 0.2 C rate, with 81.0% initial capacity retention after 50 cycles. Coating AlF3 on the particle surfaces of LiNi0.5Mn1.5O4 using a modified solid-state method can improve its electrochemical properties by enhancing its initial specific capacity from 104.6 to 109.1 mA h·g−1 and increasing its capacity retention from 80.6 to 92.1% at the 10 C rate after 100 cycles.

Lithium metal anodes (LMAs) are critical for high-energy-density batteries such as Li-S and Li-O2 batteries. The spontaneously formed solid electrolyte interface on LMAs is fragile, which may not accommodate the cyclic Li plating/stripping. This usually will result in a low coulombic efficiency (CE), short cycle life, and potential safety hazards induced by the uncontrollable growth of lithium dendrites. In this study, we fabricate a Li alginate-based artificial SEI (ASEI) layer that is chemically stable and allows easy Li ion transport on the surface of LMAs, thus enabling the stable operation of lithium metal anodes. Compared to bare LMAs, the ASEI layer-protected LMAs exhibit a more stable Li plating/stripping behavior and present effective dendrite suppression. The symmetric Li∥Li cells with the ASEI layer-protected LMAs can stably run for 850 and 350 h at current densities of 0.5 and 1 mA cm-2, respectively. Additionally, the LiFePO4∥Li full cell with the ASEI layer-protected LMA exhibits a capacity retention of about 94.0% coupled with a CE of 99.6% after 1000 cycles at 4 C. We believe that this study of engineering an ASEI brings a new and promising approach to the stabilization of LMAs for high-performance lithium metal batteries.

A multifunctional coating with high ionic and electronic conductivity is constructed on the surface of LiNi0.8Co0.1Mn0.1O2 (NCM) to boost the battery stability upon cycling and during storage as we...

Lithium-sulfur (Li-S) batteries have attracted much attention in the field of electrochemical energy storage due to their high energy density and low cost. However, the "shuttle effect" of the sulfur cathode, resulting in poor cyclic performance, is a big barrier for the development of Li-S batteries. Herein, a novel sulfur cathode integrating sulfur, flexible carbon cloth, and metal-organic framework (MOF)-derived N-doped carbon nanoarrays with embedded CoP (CC@CoP/C) is designed. These unique flexible nanoarrays with embedded polar CoP nanoparticles not only offer enough voids for volume expansion to maintain the structural stability during the electrochemical process, but also promote the physical encapsulation and chemical entrapment of all sulfur species. Such designed CC@CoP/C cathodes with synergistic confinement (physical adsorption and chemical interactions) for soluble intermediate lithium polysulfides possess high sulfur loadings (as high as 4.17 mg cm-2 ) and exhibit large specific capacities at different C-rates. Specially, an outstanding long-term cycling performance can be reached. For example, an ultralow decay of 0.016% per cycle during the whole 600 cycles at a high current density of 2C is displayed. The current work provides a promising design strategy for high-energy-density Li-S batteries.

The δ-MnO2 nanowires are fabricated and chemically bonded with the carbon black that has appropriate amounts of oxygen containing functional groups. These short δ-MnO2 nanowires are (006) crystal plane-dominated and the hybrid (δ-MnO2 nanowires/carbon black) exhibits enhanced electrocatalytic activity towards oxygen reduction reaction (ORR). The half-wave potential (0.82 V (vs. RHE)) and limiting-current density (5.47 mA cm−2) of the hybrid in alkaline medium are close to those of 20 wt% Pt/C, respectively. The hybrid is used as cathodic catalyst in a Zn-air battery cell, which displays a peak power density of 138.0 mW cm−2, comparable to that using Pt/C catalyst (142.8 mW cm−2). This excellent catalytic performance is attributed to the unique microstructure of the hybrid that accelerates the kinetics of ORR. Furthermore, the ORR catalytic mechanism is also systematically analysed based on the microstructural characterization and electrochemical response.

A composite consisting of well-dispersed and ultrafine hematite quantum-dots (∼2.7 nm) anchored on a three-dimensional ultra-porous graphene-like framework (denoted as Fe2O3-QDs–3D GF) has been designed by a facile and scalable strategy. In the composite, the ultra-porous 3D GF with high conductivity and high surface area was used as a conductive matrix with surface defective sites for the controllable growth of uniformly dispersed, ultra-small Fe2O3-QDs. The graphene framework can tightly hold a great amount of Fe2O3-QDs, thereby ensuring high utilization of active materials and the required conductivity to individual Fe2O3-QDs. The ultra-small-sized Fe2O3-QDs anchored on the 3D GF can endow the composite with a superior high surface area and enough active sites for electrochemical reactions, thus giving the composite a large specific capacitance. As expected, the as-prepared Fe2O3-QDs–3D GF electrode exhibited a high specific capacitance of 945 F g−1 at 1.0 A g−1 in a three-electrode system in 2.0 mol L−1 KOH aqueous solution. In addition, high-performance asymmetric supercapacitors have been fabricated with Fe2O3-QDs–3D GF as the anode and 3D hierarchical porous graphene (HPG) as the cathode, and they showed a very high energy density of 77.7 W h kg−1 at a power density of 0.40 kW kg−1 and maximum power density of 492.3 kW kg−1, as well as excellent cycling stability.

A peculiar nanostructure consisting of nitrogen-doped, carbon-encapsulated (N-C) SnO2@Sn nanoparticles grafted on three-dimensional (3D) graphene-like networks (designated as N-C@SnO2@Sn/3D-GNs) has been fabricated via a low-cost and scalable method, namely an in situ hydrolysis of Sn salts and immobilization of SnO2 nanoparticles on the surface of 3D-GNs, followed by an in situ polymerization of dopamine on the surface of the SnO2/3D-GNs, and finally a carbonization. In the composites, three-layer core-shell N-C@SnO2@Sn nanoparticles were uniformly grafted onto the surfaces of 3D-GNs, which promotes highly efficient insertion/extraction of Li(+). In addition, the outermost N-C layer with graphene-like structure of the N-C@SnO2@Sn nanoparticles can effectively buffer the large volume changes, enhance electronic conductivity, and prevent SnO2/Sn aggregation and pulverization during discharge/charge. The middle SnO2 layer can be changed into active Sn and nano-Li2O during discharge, as described by SnO2 + Li(+) → Sn + Li2O, whereas the thus-formed nano-Li2O can provide a facile environment for the alloying process and facilitate good cycling behavior, so as to further improve the cycling performance of the composite. The inner Sn layer with large theoretical capacity can guarantee high lithium storage in the composite. The 3D-GNs, with high electrical conductivity (1.50 × 10(3) S m(-1)), large surface area (1143 m(2) g(-1)), and high mechanical flexibility, tightly pin the core-shell structure of the N-C@SnO2@Sn nanoparticles and thus lead to remarkably enhanced electrical conductivity and structural integrity of the overall electrode. Consequently, this novel hybrid anode exhibits highly stable capacity of up to 901 mAh g(-1), with ∼89.3% capacity retention after 200 cycles at 0.1 A g(-1) and superior high rate performance, as well as a long lifetime of 500 cycles with 84.0% retention at 1.0 A g(-1). Importantly, this unique hybrid design is expected to be extended to other alloy-type anode materials such as silicon, germanium, etc.

Flexible lithium sulfur batteries are promising power sources for the next generation wearable electronics, due to their high energy density and low cost. Here, we demonstrate a metal current collector-free, binder-free, flexible sulfurized polyacrylonitrile film electrode with hollow tubular nanofibers (H-SPAN), which is fabricated via coaxial electrospinning and a simple heat treatment. The all-fibrous films H-SPAN not only provides three-dimensional continuous electron and ion transport paths, but also suppresses the shuttle effect, contributing to better redox kinetics, cycling performance, and flexibility. The H-SPAN film electrode delivers a high specific lithium storage capacity of 1250 mAh g−1sulfur or 514.75 mAh g−1electrode at 0.1C with stable cycling over 300 cycles. Additionally, when H-SPAN is applied as a cathode for room temperature Na–S batteries, it also exhibits superb capacity and cycling stability (717 mAh g−1sulfur or 295.2 mAh g−1electrode at 0.1C after 200 cycles). The working mechanism of H-SPAN is well elucidated by ex situ Raman spectroscopy and ex situ X-ray Photoelectron Spectroscopy (XPS). The excellent flexibility of the H-SPAN film electrode lends itself well to potential applications in wearable electronic devices.

Rechargeable lithium metal anodes (LMAs) with long cycling life have been regarded as the "Holy Grail" for high-energy-density lithium metal secondary batteries. The skeleton plays an important role in determining the performance of LMAs. Commercially available copper foam (CF) is not normally regarded as a suitable skeleton for stable lithium storage owing to its relatively inappropriate large pore size and relatively low specific surface area. Herein, for the first time, we revisit CF and address these issues by rationally designing a highly porous copper (HPC) architecture grown on CF substrates (HPC/CF) as a three-dimensional (3D) hierarchically bicontinuous porous skeleton through a novel approach combining the self-assembly of polystyrene microspheres, electrodeposition of copper, and a thermal annealing treatment. Compared to the CF skeleton, the HPC/CF skeleton exhibits a significantly improved Li plating/stripping behavior with high Coulombic efficiency (CE) and superior Li dendrite growth suppression. The 3D HPC/CF-based LMAs can run for 620 h without short-circuiting in a symmetric Li/Li@Cu cell at 0.5 mA cm

Graphene/nickel oxide composite (G/NiO) was synthesized through a facile hydrothermal method and subsequently microwave thermal treatment by using alcohols-reduced graphene as substrate. The as-prepared G/NiO was characterized by X-ray diffraction, Raman spectra, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscope and transmission electron microscope. The results indicate that the graphene oxide has been successfully reduced to graphene, and NiO nanoparticles are homogeneous anchored on the surface of graphene, forming a globule-on-sheet structure. The loading content of NiO nanoparticles anchoring on the surface of graphene nanosheets can be controlled by adjusting the hydrothermal temperature. The G/NiO displays superior electrochemical performance with a specific capacitance of 530 F g −1 at 1 A g −1 in 2 M of NaOH. After 5000 cycles, the supercapacitor still maintains a specific capacitance of 490 F g −1 (92% retention of the initial capacity), exhibiting excellent cycling stability.

A three-dimensional lithium iron phosphate (LiFePO4)/carbon nanotubes (CNTs)/graphene composite was successfully synthesized via solid-state reaction. The LiFePO4/carbon nanotubes/graphene (LFP–CNT–G) composite used as Li-ions battery cathode material exhibits superior high-rate capability and favorable charge–discharge cycle performance under relative high current density compared with that of LiFePO4/carbon nanotubes (LFP–CNT) composite and LiFePO4/graphene (LFP–G) composite. Graphene nanosheets and CNTs construct 3D conducting networks are favor for faster electron transfer, higher Li-ions diffusion coefficient and lower resistance during the Li-ions reversible reaction. The synergistic effect of graphene nanosheets and CNTs improves the rate capability and cycling stability of LiFePO4-based cathodes. The LFP–CNT–G electrode shows reversible capacity of 168.9 mA h g−1 at 0.2 C and 115.8 mA h g−1 at 20 C. The electrochemical impedance spectroscopy demonstrate that the LFP–CNT–G electrode has the smallest charge-transfer resistance, indicating that the fast electron transfer from the electrolyte to the LFP–CNT–G active materials in the Li-ions intercalation/deintercalation reactions owing to the three-dimensional networks of graphene and carbon nanotubes.

Conductive polypyrrole (PPy)-coated LiNi0.5Mn1.5O4 (LNMO) composites are applied as cathode materials in Li-ion batteries, and their electrochemical properties are explored at both room and elevated temperature. The morphology, phase evolution, and chemical properties of the as-prepared samples are analyzed by means of X-ray powder diffraction, thermogravimetric analysis, Raman spectroscopy, X-ray photoelectron spectroscopy and scanning and transmission electron microscopy techniques. The composite with 5 wt% polypyrrole coating shows a discharge capacity retention of 92% after 300 cycles and better rate capability than the bare LNMO electrode in the potential range of 3.5–4.9 V vs. Li/Li+ at room temperature. At the elevated temperature, the cycling performance of the electrode made from LNMO–5 wt% PPy is also remarkably stable (∼91% capacity retention after 100 cycles). It is revealed that the polypyrrole coating can suppress the dissolution of manganese in the electrolyte which occurs during cycling. The charge transfer resistance of the composite electrode is much lower than that of the bare LNMO electrode after cycling, indicating that the polypyrrole coating significantly increases the electrical conductivity of the LNMO electrode. Polypyrrole can also work as an effective protective layer to suppress the electrolyte decomposition arising from undesirable reactions between the cathode electrode and electrolyte on the surface of the active material at elevated temperature, leading to high coulombic efficiency.