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Separator plays multiple roles in the performance and safety of lithium‐ion batteries owing to the lower conductivity of the organic electrolyte and the hyperactive electrode materials. However, the commercial polyolefin separator suffers from the poor thermal stability, weak electrolyte‐wettability, low porosity as well as the demanding and costly manufacturing. Herein, we demonstrate the facial synthesis of a sponge‐like, isotropic, polyimide‐based separator by phase inversion, which possessed the higher electrolyte‐saturating conductivity (1.74 mS cm−1) and ion transference number (0.81) besides its excellent wettability and thermal stability. Meanwhile, the bearable stress was further promoted by 60 % with the 30 wt % epoxy‐strengthening tactic and the high porosity (67 %) and conductivity (1.47 mS cm−1) still preserved. Additionally, an overcharge‐sensitive PI separator was further developed by combining the conductive copolymer of coumarin‐triphenylamine by virtue of the eminent processability of PI, which demonstrated the outstanding voltage‐restraining capability for LiFePO4‐based cell during overcharge. Therefore, polyimide‐based separator could be a quite promising candidate due to its facile manufacturing, preferable performance and versatile functionalizing. [ABSTRACT FROM AUTHOR]

The solvation structure of Li+ plays a significant role in determining the physicochemical properties of electrolytes. However, to date, there is still no clear definition of the solvating power of different electrolyte solvents, and even the solvents that preferentially participate in the solvation structure remain controversial. In this study, we comprehensively discuss the solvating power and solvation process of Li+ ions using both experimental characterizations and theoretical calculations. Our findings reveal that the solvating power is dependent on the strength of the Li+‐solvent (ion‐dipole) interaction. Additionally, we uncover that the anions tend to enter the solvation sheath in most electrolyte systems through Li+‐anion (ion‐ion) interaction, which is weakened by the shielding effect of solvents. The competition between the Li+‐solvent and Li+‐anion interactions ultimately determines the final solvation structures. This insight into the fundamental understanding of the solvation structure of Li+ provides inspiration for the design of multifunctional mixed‐solvent electrolytes for advanced batteries. [ABSTRACT FROM AUTHOR]

We develop a new type of electrolyte with a high molar ratio (MR) of salt to solvent but a low molar concentration by adjusting the molar mass of the solvent. The present 1 : 2 LiFSI–triamyl phosphate electrolyte exhibits a low molar concentration of only 1.35 M along with excellent electrochemical stability against the graphite anode. [ABSTRACT FROM AUTHOR]

Li‐rich manganese based oxides (LRMOs) are considered an attractive high‐capacity cathode for advanced Li‐ion batteries; however, their poor cyclability and gradual voltage fading have hindered their practical applications. Herein, an efficient and facile strategy is proposed to stabilize the lattice structure of LRMOs by surface modification of polyacrylic acid (PAA). The PAA‐coated LRMO electrode exhibits only 104 mV of the voltage fading after 100 cycles and 88% capacity retention over 500 cycles. The structural stability is attributed to the carboxyl groups in PAA chains reacting with oxygen species on the surface of LRMO to form a uniform and tightly coated film, which significantly suppresses the dissolution of transition metal elements from the cathode materials into the electrolyte. Importantly, a H+/Li+ exchange reaction takes place between the LRMO and PAA, generating a proton‐doped surface layer. Density functional theory calculations and experimental evidence demonstrates that the H+ ions in the surface lattice efficiently inhibit the migration of transition metal ions, leading to a stabilized lattice structure. This surface modification approach may provide a new route to building a stable Li‐rich oxide cathode with high capacity retention and low voltage fading for practical Li‐ion battery applications. [ABSTRACT FROM AUTHOR]

LiMnPO4 has been attracting attention for high energy density (701 Wh kg−1) and excellent safety. However, LiMnPO4 suffers from the cycling instability coming from the fragile solid electrolyte interface, besides the Jahn-Teller effect of Mn3+, the poor electrical conductivity and the sluggish ionic conductivity. The substitution of cation with less ionic radius for Mn2+ is conducive to stabilize the solid-electrolyte interface and retard the erosion from electrolyte; therefore, the gradient Co-doped LiMn0.98Co0.02PO4 was synthesized with 25.93 (mol) % Co on the surface by the secondary solvothermal method, and the permeated depth reaches more than 20 nm because of the coprecipitation and cation exchange of Co2+ and Mn2+. LiMn0.98Co0.02PO4/Li cell that demonstrates the cycling performance is remarkably enhanced with 87% capacity retention after 380 cycles at room temperature, even 87% after 100 cycles at 60 °C. Meanwhile, the preferential growth along the a–c plane results in the highly [010]-oriented LiMnPO4 by the solvothermal, which afford more channels for Li+ migration by exposing more reaction sites, and the infrared spectrum also reflects the less Mn2+-Li+ antisite defects in the crystal. So the samples show the superior rate performance as well. [ABSTRACT FROM AUTHOR]

Li2FeSiO4 is a low-cost, environmentally friendly electrode material with high theoretical capacity. However, obtaining pure-phase Li2FeSiO4 on a large scale is difficult. In this study, pure Li2−xFeSi1−xPxO4/C is prepared easily by using the low cost compound Fe(NO3)3·9H2O, with the help of citric acid and appropriate ratios of NH4H2PO4 (x = 0.03–0.15). The possible mechanism of the system with NH4H2PO4 to synthesize Li2−xFeSi1−xPxO4/C is that there is a catalysis process in the system, which helps to produce H2, providing a reducing environment in every particle of the reactants guaranteeing a complete change from Fe3+ to Fe2+. The produced H2 is verified by the gas chromatography of the collected gas produced in the calcination process. The ratios of NH4H2PO4 in this system could adjust the valence of element Fe in the products. Without NH4H2PO4, an Fe2O3 impurity is formed accompanying the Li2FeSiO4. With the addition of 1 at% NH4H2PO4, the Li4SiO4 impurity accords with the objective Li2−xFeSi1−xPxO4/C. Also, Fe with zero-valence could be found as an impurity with the addition of 20 at% NH4H2PO4 due to overreduction in the system. The synthesized pure Li2−xFeSi1−xPxO4/C (x = 0.03) displayed the highest discharge capacity of 179 mA h g−1 in the first cycle, the best discharge capacity retention and the most reliable redox reversibility of the coulombic efficiency (approximately 100%), compared with the synthesized materials with Fe2O3 or Li4SiO4 impurities. [ABSTRACT FROM AUTHOR]

The novel phosphate derivatives of phosphaphenanthrene with high-density phosphorus were synthesized and used as flame retardant additives for Li-ion batteries. The structures of compounds were characterized by H NMR, C NMR, P NMR, FT-IR, and HR-MS. The excellent thermal stability of compounds was ascertained by thermogravimetric analysis and differential scanning calorimetry. The compounds were added to conventional electrolytes as flame retardant additives and evaluated their ionic conductivity, electrochemical stability, self-extinguishing properties, and combustion performance. The results showed that the compound containing higher phosphorus content has efficient flame retardant properties. [ABSTRACT FROM AUTHOR]

The cross-linking gel copolymer electrolytes containing alkyl acrylates, triethylene glycol dimethacrylate, and liquid electrolyte were prepared by in situ thermal polymerization. The gel polymer electrolytes containing 15 wt% polymer content and 85 wt% liquid electrolyte content with sufficient mechanical strength showed the high ionic conductivity around 5 × 10 Scm at room temperature. The gel electrolytes containing different polymer matrices were prepared, and their physical observation and conductivity were discussed carefully. The cross-linking copolymer gel electrolytes of alkyl acrylates with other monomers were designed and synthesized. The results showed that copolymerization can improve the mechanical properties and ionic conductivities of the gel electrolytes. The polymer matrices of gels had excellent thermal stability and electrochemical stability. The scanning electron microscope analysis showed the gel electrolyte was the homogeneous structure, and the cross-linking polymer host was the porous three-dimensional network structure, which demonstrated the high conductivity of the gel electrolytes. The gel polymer Li-ion battery was prepared by this in situ thermal polymerization. The cell exhibited high charge-discharge efficiency at 0.1 C. The results of LiFePO4-PEA-Li cell and graphite-PEA-Li cell showed that gel polymer electrolytes have good compatibility with the battery electrodes materials. [ABSTRACT FROM AUTHOR]

The structure and phase evolution characteristics of the Na 6-2 x Fe x (SO 4) 3 (1.5≤x≤2.0) system are comprehensively investigated by both experimental and computational methods. It reveals that a pure phase exists in the 1.6≤ x ≤1.7 region, and part of Na ions tend to occupy Fe sites to form more stable frameworks. The NFSO-1.7 exhibits the best electrochemical performance among the NFSO- x samples, delivering a high discharge capacity (104.5 mAh g−1 at 0.1C), excellent rate performance (81.5 mAh g−1 at 30C), and remarkable cycle stability over 10,000 cycles with a high-capacity retention rate of 72.4%. [Display omitted] Fe-based polyanionic sulfate materials are one of the most promising candidates for large-scale applications in sodium-ion batteries due to their low cost and excellent electrochemical performance. Although great achievements have been gained on a series of Na 6−2 x Fe x (SO 4) 3 (NFSO- x , 1.5 ≤ x ≤ 2.0) materials such as Na 2 Fe 2 (SO 4) 3 , Na 2 Fe 1.5 (SO 4) 3 , and Na 2.4 Fe 1.8 (SO 4) 3 for sodium storage, the phase and structure characteristics on these NFSO- x are still controversial, making it difficult to achieve phase-pure materials with optimal electrochemical properties. Herein, six NFSO- x samples with varied x are investigated via both experimental methods and density functional theory calculations to analyze the phase and structure properties. It reveals that a pure phase exists in the 1.6 ≤ x ≤ 1.7 region of the NFSO- x , and part of Na ions tend to occupy Fe sites to form more stable frameworks. The NFSO-1.7 exhibits the best electrochemical performance among the NFSO- x samples, delivering a high discharge capacity (104.5 mAh g−1 at 0.1 C, close to its theoretical capacity of 105 mAh g−1), excellent rate performance (81.5 mAh g−1 at 30 C), and remarkable cycle stability over 10,000 cycles with high-capacity retention of 72.4%. We believe that the results are useful to clarify the phase and structure characteristics of polyanionic materials to promote their application for large-scale energy storage. [ABSTRACT FROM AUTHOR]

The nonflammable gel polymer electrolytes have become one of the most desirable alternatives among various electrolytes for the fabrication of stable advanced LIBs. Acryloyloxyethyl dialkyl phosphates which combine the good polymerization capability of acrylate and flame retardant properties of phosphates are designed and synthesized. The polymerization capability including the copolymerization ability of these compounds is compared with allyl phosphonate/phosphates and shows better polymerization capability than the allyl phosphonate/phosphates due to the separation of ethylenedioxy between the double bond and the phosphoryl group. The corresponding cross-linking gel polymer electrolytes with good mechanical property are prepared by in-situ radical thermal polymerization. The gel copolymer electrolytes have good thermal stability with the onset decomposition temperature above 220 °C, efficient flame retardant with low content of 5 wt%, good electrochemical stability of up to 4.5 V (vs. Li+/Li) and high ionic conductivity over 7 mS cm−1. The LiFePO 4 /GPE/Li cell shows good cycling performance and high coulombic efficiency. The coordination interaction is existed between acryloyloxyethyl dialkyl phosphate and lithium ion, which is testified by FT-IR, 31P NMR and HRMS. Unlabelled Image • The polymerization capabilities of different alkenyl phosphates were compared. • The gel polymer electrolytes have high ionic conductivity and flame ratardancy. • The gel polymer electrolyte based lithium ion cells have good cycling performance. • There is attractive interaction between alkenyl phosphate and lithium ion. [ABSTRACT FROM AUTHOR]

Abstract As the pivotal component, separators play the important role in electrochemical performance and even determine the safety of batteries to a great extent. Here, a kind of modified polyacrylonitrile/silica-aerogel (M-PSA) as high-safety separator for lithium/sodium-ion battery is reported, which is obtained as follows: the polyacrylonitrile (PAN) nonwoven prepared through electrospinning, is modified by hydrolysis of its nitrile group and then, in-situ growth of silica-aerogel on it. The as-synthesized M-PSA can enhance the chemical stability in conventional electrolytes, such as ethylene carbonate/propylene carbonate (EC/PC), ethylene carbonate/methyl-carbonate (EC/DMC) and diglyme. It shows high porosity and excellent affinity to these conventional electrolytes. More importantly, the M-PSA separator could hold its structural integrity at 250 °C and no severe shrinkage at 350 °C (80.06% of separator area retention) indicating excellent thermal stability. Electrochemical measurements of the M-PSA separator are tested in lithium battery and sodium battery (half cells and full cells), respectively, exhibiting good cycle performance and fast kinetics. The M-PSA separator is promising as high-safety separator for advanced lithium/sodium-ion batteries for widely applications. Graphical abstract fx1 Highlights • A new M-PSA separator is prepared by growth of silica-aerogel on hydrolyzed PAN nonwoven. • This M-PSA separator exhibits high heat-resistant temperature of 280 °C (no shrinkage). • This composite separator possesses excellent wettability for conventional electrolyte. • The Li/Na-ion batteries with the separator exhibit good cycle performance and fast kinetics. [ABSTRACT FROM AUTHOR]

Separator as an important part of lithium-ion batteries, allowing the ion to transfer and preventing the direct contact of anode with cathode, determines the safety of the batteries. In this work, a kind of polypropylene/hydrophobic silica-aerogel-composite (SAC) separator is fabricated through combining hydrophobic silica aerogel and polypropylene (PP) separator. The rationally designed SAC effectively increases the thermal stability of the separator with slightly growing weight (the area retention rate is 30% higher than that of the PP separator after being heated for 30 min at 160 °C). In addition, the hydrophobic silica aerogel layer in SAC significantly improves the wettability of PP separator to electrolyte owning to the introduced hydrophobic functional groups of -Si(CH 3 ) 3 and porous structure, and the contact angles of SAC separator to several common organic electrolytes (EC/DMC, DMC/DOL, Diglyme) are close to 0°. Electrochemical tests show that the prepared SAC separator can decrease the polarization of Li-ion batteries and leads to improved power performance and cycle stability. And the SAC separator is firm with neglectable abscission after folding 200 times. This work provides a new way to improve the safety and simultaneously reduce the polarization of the batteries, implying promising application potential in power batteries. [ABSTRACT FROM AUTHOR]

A series of spherical hierarchical LiNi 1 − x − y Co x Al y O 2 (0 < x, y < 0.2) were successfully synthesized via a novel and simple cation exchange process. Specifically, spherical flowerlike Ni 1 − x − y Co x Al y (OH) 2 + y (0 < x, y < 0.2) were obtained from (Ni 0.85 Co 0.15 ) 3 (NO 3 ) 2 (OH) 4 via the cation exchange between Al ion and Ni/Co ions while maintaining its morphology. Then, after calcination, the hierarchical spherical LiNi 1 − x − y Co x Al y O 2 (0 < x, y < 0.2) could be easily obtained. Among these materials, the hierarchical spherical LiNi 0.84 Co 0.14 Al 0.02 O 2 performs the discharge capacity of 190 mAh g −1 at 20 mA g −1 at the second cycle, while the material LiNi 0.85 Co 0.15 O 2 obtained using the (Ni 0.85 Co 0.15 ) 3 (NO 3 ) 2 (OH) 4 without ion exchange performs a discharge capacity of 165 mAh g −1 . Furthermore, the hierarchical spherical LiNi 0.84 Co 0.14 Al 0.02 O 2 maintains the high capacity retention of 84.0% after 225 cycles at 200 mA g −1 . This work exploits a new and facile way to synthesize high capacity Al-contained layered metal oxides cathode materials. [ABSTRACT FROM AUTHOR]