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The preferentially selective extraction of Li + from spent layered transition metal oxide (LiMO 2 , M = Ni, Co, Mn, etc.) cathodes has attracted extensive interest based on economic and recycling efficiency requirements. Presently, the efficient recycling of spent LiMO 2 is still challenging due to the element loss in multistep processes. Here, we developed a facile strategy to selectively extract Li + from LiMO 2 scraps with stoichiometric H 2 SO 4 . The proton exchange reaction could be driven using temperature, accompanied by the generation of soluble Li 2 SO 4 and MOOH precipitates. The extraction mechanism includes a two-stage evolution, including dissolution and ion exchange. As a result, the extraction rate of Li + is over 98.5% and that of M ions is less than 0.1% for S-NCM. For S-LCO, the selective extraction result is even better. Finally, Li 2 CO 3 products with a purity of 99.68% can be prepared from the Li + -rich leachate, demonstrating lithium recovery efficiencies as high as 95 and 96.3% from NCM scraps and S-LCO scraps, respectively. In the available cases, this work also represents the highest recycling efficiency of lithium, which can be attributed to the high leaching rate and selectivity of Li + , and even demonstrates the lowest reagent cost. The regenerated LiNi 0.5 Co 0.24 Mn 0.26 O 2 and Na 1.01 Li 0.001 Ni 0.38 Co 0.18 Mn 0.44 O 2 cathodes also deliver a decent electrochemical performance for Li-ion batteries (LIBs) and Na-ion batteries (NIBs), respectively. Our current work offers a facile, closed-loop, and scalable strategy for recycling spent LIB cathodes based on the preferentially selective extraction of Li + , which is superior to the other leaching technology in terms of its cost and recycling yield.

The low-cost and profusion of sodium reserves make Na-ion batteries (NIBs) a potential candidate to lithium-ion batteries for grid-scale energy storage applications. NaVOPO 4 has been recognized as one of the most promising cathodes for high-energy NIBs, owing to their high theoretical capacity and energy density. However, their further application is hindered by the multiphase transition and conductivity confinement. Herein, we proposed a feasible, one-step hydrothermal synthesis to regulate the synthesis of α-NaVOPO 4 with controlled morphologies. The electrochemical properties of the NaVOPO 4 electrode can be significantly enhanced taking Ketjen black (KB) as the optimized conductive carbon. Besides, combining with the nanocrystallization and construction of the conductive framework via high-energy ball milling, taking KB as the conductive carbon, the as-prepared NaVOPO 4 /5%KB exhibits superior Na-storage performance (140.2 mA h g -1 at 0.1 C and a capacity retention of 84.8% over 1000 cycles at 10 C) to the original NaVOPO 4 (128.5 mA h g -1 at 0.1 C and a capacity retention of 83.1% over 1000 cycles at 10 C). Moreover, the aqueous full cell with NaTi 2 (PO 4 ) 3 as the anode delivers a capacity of 114.7 mA h g -1 at 0.2 C (141 W h kg -1 energy density) and 80.6% capacity retention over 300 cycles at 5 C. The excellent electrochemical performance can be attributed to the nanosized structural and enhanced interfacial effect, which could be rewarding to construct electron transportation tunnels, thus speeding up the Na + -diffusion kinetics. The modified strategy provides an efficient approach to intensify the electrochemical performance, which exhibits potential application of the NaVOPO 4 cathode for NIBs.

The air-sensitivity of transition metal oxide cathode materials (Na x TMO 2 , TM: transition metal) is a challenge for their practical application in sodium-ion batteries for large-scale energy storage. However, the deterioration mechanism of Na x TMO 2 under ambient air is unclear, which hinders the precise design of air-stable Na x TMO 2 . Here, we revealed the origin of Na x TMO 2 degradation by capturing the initial degradation status and microstructural evolution under ambient atmospheres with optimal humidity. It was found that the insertion of CO 2 into Na layers along (003) planes of Na x TMO 2 led to initial growth of Na 2 CO 3 nanoseeds between TM layers, which initiated fast structure degradation with surface cracks and extrusion of Na 2 CO 3 out of Na x TMO 2 . The degradation extents and pathways for Na x TMO 2 could be highly associated with crystal orientation, particle morphology, and ambient humidity. Interestingly, the deteriorated Na x TMO 2 could be completely healed through optimal recalcination, showing even improved air-stability and electrochemical performance. This work provides a helpful perspective on the interfacical structure design of high-performance Na x TMO 2 cathodes for sodium-ion batteries.

Na-ion batteries (NIBs) have been considered as potential candidates for large-scale energy storage, where O3-type Na-based layered oxide cathodes have attracted great attention due to their high capacity and low cost. However, O3-Na x TMO 2 materials still suffer from insufficient air stability, which could lead to deteriorative electrochemical properties and thus hinder their practical application. In this work, a series of Al-doped O3-NaFe (1/3- x ) Ni 1/3 Mn 1/3 Al x O 2 cathodes prepared by a co-precipitation method were investigated to enhance their electrochemical performance and air stability through stabilizing their structural and interface chemical properties. The Al-doped O3 - NaFe (1/3-0.01) Ni 1/3 Mn 1/3 Al 0.01 O 2 (NFNMA 0.01 ) cathode delivers a comparable capacity of 138 mAh g -1 and keeps a capacity retention of 85.88% after 50 cycles at 0.2 C, while the undoped O3 - NaFe 1/3 Ni 1/3 Mn 1/3 O 2 (NFNM) can only keep a capacity retention of 71.02%, although with an initial capacity of 141 mAh g -1 at 0.2 C. For the air stability, the capacity decay rates are 58.87 and 5.07% for the undoped NFNM and Al-doped NFNMA 0.01 after the air exposure for 30 days, respectively. The greatly decaying electrochemical performance could be due to the formation of carbonates during air exposure, which can be efficiently suppressed by Al doping. The doped Al 3+ has been confirmed to be inserted into the NFNM crystal lattice, inducing the reduced values of lattice parameters a and c due to the smaller ionic radius of Al 3+ (53.5 pm) vs Fe 3+ (55.0 pm). This study demonstrates that Al doping plays an important role in the air stability and cycling stability for layered cathode materials, which offers an efficient strategy to optimize the material design for their practical application in NIBs.

Prussian blue analogues (PBAs) are considered to be ideal multivalent cation host materials due to their unique open-framework structure. In aqueous solution, however, the PBAs' cathodes have a low reversible capacity limited by the single electrochemical group Fe(CN) 6 3- and high crystal water content. They also suffer from fast cycle fading, resulting from significant oxygen/hydrogen evolution and cathode dissolution. In this work, a high-capacity PBA-type FeFe(CN) 6 cathode with double transition metal redox sites is successfully demonstrated in 5 m Al(CF 3 SO 3 ) 3 Water-in-Salt electrolyte (Al-WISE). Due to Al-WISE having a wide electrochemical window (2.65 V) and low dissolution of the cathode, our PBA cathode exhibits a high discharge capacity of 116 mAh/g and the superior cycle stability >100 cycles with capacity fading of 0.39% per cycle.

Solid-state electrolytes are actively sought for their potential application in energy storage devices, especially lithium metal rechargeable batteries. However, one of the key challenges in the development of solid-state electrolytes is their lower ionic conductivity compared with that of liquid electrolytes (10 -2 S cm -1 at room temperature), where a large gap still exists. Therefore, the pursuit of high ionic conductivity equal to that of liquid electrolytes remains the main objective for the design of solid-state electrolytes. Here, we show a series of high-charge density polymerized ionic networks as solid-state electrolytes that take inspiration from poly(ionic liquid)s. The obtained quasi-solid electrolyte slice displays an astonishingly high ionic conductivity of 5.89 × 10 -3 S cm -1 at 25 °C (the highest conductivity among those of the state-of-art polymer gel electrolytes and polymer solid electrolytes) and ultrahigh decomposition potential, >5.2 V versus Li/Li + , which are attributed to the continuous ion transport channel formed by an ultrahigh ion density and an enhanced chemical stability endowed by highly cross-linked networks. The Li/LiFePO 4 and Li/LiCoO 2 batteries (3.0-4.4 V) assembled with the solid electrolytes show high stable capacities of around 155 and 130 mAh g -1 , respectively. In principle, our work breaks new ground for the design and fabrication of the solid-state electrolytes in various energy conversion devices.

As candidates for high-energy density cathodes, lithium-rich (Li-rich) layered materials have attracted wide interest for next-generation Li-ion batteries. In this work, surface functionalization of a typical Li-rich material Li 1.2 Mn 0.56 Ni 0.17 Co 0.07 O 2 is optimized by fluorine (F)-doped Li 2 SnO 3 coating layer and electrochemical performances are also enhanced accordingly. The results demonstrate that F-doped Li 2 SnO 3 -modified material exhibits the highest capacity retention (73% after 200 cycles), with approximately 1.2, 1.4, and 1.5 times of discharge capacity for Li 2 SnO 3 surface-modified, F-doped, and pristine electrodes, respectively. To reveal the fundamental enhancement mechanism, intensive surface Li + diffusion kinetics, postmortem structural characteristics, and aging tests are performed for four sample systems. The results show that the integrated coating layer plays an important role in addressing interface compatibility, not only limited in stabilizing the bulk structure and suppressing side reactions, synergistically contributing to the performance enhancement for the active electrodes. These findings not only pave the way to commercial application of the Li-rich material but also shed new light on surface modification in batteries and other energy storage fields.

Nanosized Na 3 PS 4 solid electrolyte with an ionic conductivity of 8.44 × 10 -5 S cm -1 at room temperature is synthesized by a liquid-phase reaction. The resultant all-solid-state FeS 2 /Na 3 PS 4 /Na batteries show an extraordinary high initial Coulombic efficiency of 95% and demonstrate high energy density of 611 Wh kg -1 at current density of 20 mA g -1 at room temperature. The outstanding performances of the battery can be ascribed to good interface compatibility and intimate solid-solid contact at FeS 2 electrode/nanosized Na 3 PS 4 solid electrolytes interface. Meanwhile, excellent cycling stability is achieved for the battery after cycling at 60 mA g -1 for 100 cycles, showing a high capacity of 287 mAh g -1 with the capacity retention of 80%.

Rechargeable sodium-ion batteries have drawn increasing attention as candidates for the post lithium-ion batteries in large-scale energy storage systems. Layered oxides are the most promising cathode materials and their pure phases (e.g., P2, O3) have been widely investigated. Here we report a series of cathode materials with O3/P2 hybrid phase for sodium-ion batteries, which possesses advantages of both P2 and O3 structures. The designed material, Na 0.78 Ni 0.2 Fe 0.38 Mn 0.42 O 2 , can deliver a capacity of 86 mAh g -1 with great rate capability and cycling performance. 66% capacity is still maintained when the current rate reaches as high as 10C, and the capacity retention is 90% after 1500 cycles. Moreover, in situ XRD was performed to examine the structure change during electrochemical testing in different voltage ranges, and the results demonstrate 4 V as the optimized upper voltage limit, with which smaller polarization, better structural stability, and better cycling performance are achieved. The results obtained here provide new insights in designing cathode materials with optimal structure and improved performance for sodium-ion batteries.

A facile one-pot hydrothermal strategy is applied to prepare Co and F codoped SnO 2 (Co-F/SnO 2 ) nanoparticles, which exhibit a unique rice-shaped self-similar structure. Compared with the pristine and Co-doped counterparts (SnO 2 and Co/SnO 2 ), the Co-F/SnO 2 electrode demonstrates higher capacity, better cyclability, and rate capability as anode material for lithium ion batteries (LIBs). A high charge capacity of 800 mAh g -1 can be successfully delivered after 50 cycles at 0.1 C, and a high reversible capacity of 700 mAh g -1 could be retained after 100 cycles at 5 C. The excellent lithium storage performances of the Co-F/SnO 2 nanoparticles could be attributed to the synergetic effects of the doped Co and F, as well as the unique hierarchical self-similar structure with moderate oxygen defect and inactive pillars, which not only facilitates the fast diffusion of Li ions, but also stabilizes the structure during the electrochemical cycling.

Lithium (fluorosulfonyl)(n-nonafluorobutanesulfonyl)imide [Li[(FSO 2 )(n-C 4 F 9 SO 2 )N] (LiFNFSI)] is investigated as a conducting salt, which can form a relatively stable solid-electrolyte-interphase film in concentrated ether electrolyte to achieve favorable protection for lithium metal anodes. Li|Cu and Li|Li cells with concentrated LiFNFSI-based electrolyte have been demonstrated to display high average Coulombic efficiency (≈97%) and excellent cycling stability (over 1,000 h) of metallic lithium anodes, compared to concentrated lithium bis(trifluoromethanesulfonyl)imide [Li[N(SO 2 CF 3 ) 2 ] (LiTFSI)]-based electrolyte. The morphologies and compositions of the lithium-metal anode surface are also comparatively analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. Moreover, superior electrochemical performance in the concentrated LiFNFSI-based electrolyte for Li|LiFePO 4 cells is also presented herein. These results indicate that concentrated LiFNFSI-based electrolyte is a promising candidate for metallic lithium rechargeable batteries.

A non-sintered method with toothpaste electrode for improving electrode ionic conductivity and reducing interface impedance is introduced in solid-state rechargeable batteries. At 70 °C, this novel solid-state battery can deliver a capacity of 80 mAh g -1 in a voltage range of 2.5-3.8 V at 0.1C rate using layered oxide Na 0.66 Ni 0.33 Mn 0.67 O 2 , Na-β″-Al 2 O 3 and sodium metal as cathode, electrolyte and anode, respectively. Moreover, the battery shows a superior stability and high reversibility, with a capacity retention of 90% after 10 000 cycles at 6C rate and a capacity of 79 mAh g -1 is recovered when the current rate is returned to 0.1C. Furthermore, a very thick electrode with active material mass loading of 6 mg cm -2 also presents a reasonable electrochemical performance. These results demonstrate that this is a promising approach to solve the interface problem and would open a new route in designing the next generation solid-state battery.

Solid polymer electrolytes (SPEs) would be promising candidates for application in high-energy rechargeable lithium (Li) batteries to replace the conventional organic liquid electrolytes, in terms of the enhanced safety and excellent design flexibility. Herein, we first report novel perfluorinated sulfonimide salt-based SPEs, composed of lithium (trifluoromethanesulfonyl)(n-nonafluorobutanesulfonyl)imide (Li[(CF 3 SO 2 )(n-C 4 F 9 SO 2 )N], LiTNFSI) and poly(ethylene oxide) (PEO), which exhibit relatively efficient ionic conductivity (e.g., 1.04 × 10 -4 S cm -1 at 60 °C and 3.69 × 10 -4 S cm -1 at 90 °C) and enough thermal stability (>350 °C), for rechargeable Li batteries. More importantly, the LiTNFSI-based SPEs could not only deliver the excellent interfacial compatibility with electrodes (e.g., Li-metal anode, LiFePO 4 and sulfur composite cathodes), but also afford good cycling performances for the Li|LiFePO 4 (>300 cycles at 1C) and Li-S cells (>500 cycles at 0.5C), in comparison with the conventional LiTFSI (Li[(CF 3 SO 2 ) 2 N])-based SPEs. The interfacial impedance and morphology of the cycled Li-metal electrodes are also comparatively analyzed by electrochemical impedance spectra and scanning electron microscopy, respectively. These indicate that the LiTNFSI-based SPEs would be potential alternatives for application in high-energy solid-state Li batteries.