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All‐solid‐state lithium batteries (ASSBs) enabled by solid‐state electrolytes (SEs) including oxide‐based and sulfide‐based electrolytes have gained worldwide attention because of their intrinsic safety and higher energy density over conventional lithium‐ion batteries (LIBs). However, despite the high ionic conductivity of advanced SEs, ASSBs still exhibit high overall internal resistance, the most significant contributor of which can be ascribed to the cathode‐SE interfaces. This review seeks to clarify the critical issues regarding the cathode‐SE interfaces, including fundamental principles and corresponding solutions. First, major issues concerning electro‐chemo‐mechanical instability between cathodes and SEs and their formation mechanisms are discussed. Then, specific problems in oxides and sulfides and various solutions and strategies toward interfacial modifications are highlighted. Efforts toward the characterization and analysis of cathode‐SE interfaces with advanced techniques are also summarized. Finally, perspectives are offered on several problems demanding urgent solutions and the future development of SE applications and ASSBs. [ABSTRACT FROM AUTHOR]

As a promising candidate of current solid-state electrolytes with various advantages, such as broad electrochemical stability window, high thermal stability, and chemical stability, garnet-type solid-state electrolyte Li7La3Zr2O12 (LLZO) attracts extensive research attention. Researchers usually use the element doping method to improve the lithium ion conductivity of LLZO and to stabilize the cubic phase. However, the improvements either increase the cost of raw materials or need complex process. In this work, the preparation process of Al-doped LLZO is optimized by a simple post-doping method (LLZO-Al), and the as-prepared LLZO-Al shows a high lithium ion conductivity of 5.331 × 10−4 S cm−1 and an activation energy of 0.25 eV at room temperature. In addition, the LLZO-Al exhibits excellent stability against Li in LiǁLLZO-AlǁLi symmetric cell, and the LiNi0.8Co0.1Mn0.1O2 (NCM811)ǁLLZO-AlǁLi solid-state cell delivers a stable cycle of 120 cycles at 0.1C. This work offers a low-cost preparation method of LLZO-based solid-state electrolytes with high ionic conductivities for high-energy solid-state lithium metal batteries. [ABSTRACT FROM AUTHOR]

Solid polymer electrolyte with good thermal stability and flexibility is an excellent candidate for solid‐state lithium metal batteries, while its low ionic conductivity caused by high crystallinity limits its application at ambient temperature. Here a metal organic framework (zeolitic imidazolate framework‐8, ZIF‐8) composited comb‐like methoxy poly(ethylene glycol) acrylate polymer electrolyte (MCPE) with high ionic conductivity (9.96 × 10−5 S cm−1 at 30 °C) is prepared by an in situ UV polymerization method. The as‐prepared MCPE exhibits improved mechanical property due to the introduction of porous ZIF‐8 nanofillers, which is beneficial to suppress the growth of lithium dendrites. Consequently, the LiFePO4||MCPE||Li cells show a high capacity of 116 mAh g−1 at 30 °C and 0.5 C, and maintain 89.4% of initial capacity after 150 cycles with the average Coulombic efficiency of 99.9%. These results demonstrate that the MCPE shows great potential in solid‐state lithium metal batteries near room temperature. [ABSTRACT FROM AUTHOR]

Cryogenic transmission electron microscopy (cryo-TEM) is a valuable tool recently proposed to investigate battery electrodes. Despite being employed for Li-based battery materials, cryo-TEM measurements for Na-based electrochemical energy storage systems are not commonly reported. In particular, elucidating the chemical and morphological behavior of the Na-metal electrode in contact with a non-aqueous liquid electrolyte solution could provide useful insights that may lead to a better understanding of metal cells during operation. Here, using cryo-TEM, we investigate the effect of fluoroethylene carbonate (FEC) additive on the solid electrolyte interphase (SEI) structure of a Na-metal electrode. Without FEC, the NaPF6-containing carbonate-based electrolyte reacts with the metal electrode to produce an unstable SEI, rich in Na2CO3 and Na3PO4, which constantly consumes the sodium reservoir of the cell during cycling. When FEC is used, the Na-metal electrode forms a multilayer SEI structure comprising an outer NaF-rich amorphous phase and an inner Na3PO4 phase. This layered structure stabilizes the SEI and prevents further reactions between the electrolyte and the Na metal. The solid electrolyte interphase (SEI) strongly affects the cycling behaviour of rechargeable alkali metal cells. Here, the authors investigate via cryo-electron microscopy the SEI formed on a Na metal electrode using fluoroethylene carbonate-containing electrolyte. [ABSTRACT FROM AUTHOR]

Gel polymer electrolytes (GPEs) hold great promise for lithium (Li) metal batteries (LMBs). Nevertheless, a critical challenge lies in reducing the thickness of GPEs while maintaining their mechanical integrity to achieve high‐energy‐density LMBs. Additionally, protecting the Li metal anode via electrolyte engineering in GPEs remains demanding. Herein, an innovative ultrathin (1 µm‐thick) yet robust GPE developed using an in situ curing technique, featuring a nanofibrous, exceptionally strong polyethylene separator is presented. The unique microstructure, interfacial conformability, and ultrahigh mechanical robustness of the ultrathin polyethylene separator are thoroughly verified. Enhanced ionic association within the GPE is achieved due to the strong affinity of electrolyte solvent with the fluorinated polymer network, as confirmed by large‐scale molecular dynamics simulations. The optimized solvation structure with high contact ion pairs and aggregate fractions contributes to forming an anion‐derived inorganic‐rich solid electrolyte interphase (SEI), thereby protecting the lithium anode. Benefiting from the ultrahigh robustness of GPE and the excellent interfacial stability, the Li metal full cell with a high mass loading LiNi0.8Co0.1Mn0.1O2 cathode (≈17.3 mg cm−2) and thin Li foil anode (50 µm) demonstrates 91% capacity retention after 200 cycles. This design demonstrates a feasible approach toward the practical quasi‐solid‐state LMBs. [ABSTRACT FROM AUTHOR]

The PE separator modified by double-coated nano-sized LLZTO is developed. Benefiting from the double-coated nano-sized LLZTO layer's enhancement to thermal stability and it can guide the uniform deposition of lithium ions and suppress the growth of lithium dendrites, an excellent electrochemical performance could be achieved in the lithium symmetric cell and lithium metal batteries. [Display omitted] • The PE separator modified by double-coated nano-sized LLZTO is developed. • The nano-sized LLZTO improves the thermal stability of the PE separator. • It can also guide the uniform Li ions deposition and suppress Li dendrites lithium. • Symmetric and full cells with LLZTO-coated separator exihibit an excellent performance. Lithium metal batteries, as one of high-energy-density batteries, have become the hot spot for numerous researchers. However, serious safety problems caused by lithium dendrites need to be urgently addressed. In this work, we introduce nano-sized garnet solid-state electrolyte Li 6.75 La 3 Zr 1.75 Ta 0.25 O 12 (LLZTO) to fabricate a high-safety thin composite solid electrolyte membrane (20 μm) that is simple in process and facile in preparation conditions. The thin composite solid electrolyte film has better wrinkle resistance than ordinary polyethylene (PE) films and can guide the uniform deposition of lithium ions and suppress the growth of lithium dendrites. The thermal stability of the PE separator modified by double-coated nano-sized LLZTO is enhanced, which exhibits only 30 % shrinking percentage at 140 °C in comparison with 90 % of ordinary PE. The lithium symmetric cell with the nano-sized garnet solid-state electrolyte modified separator is relatively stable after 1000 h cycling at the current density of 1 mA cm−2. More importantly, after adding the adaptable electrolyte, the lithium metal battery assembled with modified separator can be maintained for 150 cycles (0.2C) stably with a high cathode active material loading of NCM811 (18 mg cm−2), and can maintain above 95 % Coulombic efficiency on average. Our work provides a pathway for the preparation of superior thermal stability and high safety garnet-based composite membranes towards lithium metal batteries. [ABSTRACT FROM AUTHOR]

Solid electrolyte with stable and fast Na + ionic conductivity is of central importance in the development of all-solid-state sodium batteries. Here we present a novel Na + conductor based on complex hydrides with composition of Na 3 NH 2 B 12 H 12 . It exhibits remarkable thermal stability up to 593 K and excellent electrochemical stable window up to 10 V (vs. Na + /Na). It demonstrates a high Na + conductivity of 1.0 × 10 −4  S cm -1  at a temperature of 372 K, which is much higher than those of its precursors NaNH 2 and Na 2 B 12 H 12 . All-solid-state Na-ion batteries were constructed by employing the obtained Na 3 NH 2 B 12 H 12 as electrolyte, TiS 2 as cathode and sodium foil as anode, which can reversibly discharge/charge for over 200 cycles with more than 50% capacity retention at temperature of 353 K and a rate of 0.1 C. This work opens the gate to develop advanced solid electrolytes via combination of metal amides with closo borates. [ABSTRACT FROM AUTHOR]

LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) cathode coupling with artificial graphite (AG) is a promising tendency for high-energy-density batteries. However, realization of long-term lifespan under current realistic conditions remains a "Gordian knot" for large-scale commercialization-oriented realm owing to the aggressive and highly reactive Ni4+ sites on the delithiated cathodes and electrolyte exhaustion. Vinylene carbonate (VC) is commonly employed as the additive for graphite anode in carbonate electrolytes. However, VC has limited protection ability for NCM811/AG, especially for high-temperature cycling, showing conspicuous gas generation and large interfacial resistance. Herein, advanced carbonate-based electrolytes containing vinylene carbonate (VC) and phosphate compounds like triallyl phosphate (TPPC2) and tripropargyl phosphate (TPPC3) as electrolyte additives are reported to improve the performance of NCM811/AG pouch cells at elevated temperature. Theoretical calculations and comprehensive characterizations reveal that these two electrolytes well regulate the electrodes interface with more robust and homogenous films. Moreover, the TPPC2 and TPPC3 additives exhibit stronger tendency to eliminate the corrosive active oxygen (1O 2) released from NCM811. These merits mitigate the electrolyte decomposition, decrease the gas generation, inhibit the dissolution of transition metals from cathode, and protect the structure stability of NCM811. Such outstanding electrochemical performance reveals promising prospects in the commercialized application of NCM811/AG batteries. ● Advanced carbonate electrolyte is prepared with VC and unsaturated phosphate. ● VC and unsaturated phosphate are beneficial for generating polymer-rich CEI. ● Capacity retention of NCM811/AG cells is 90.5% after 500 cycles at 1.0 C and 55 °C. ● DEMS is used to investigate gas evolution from a new perspective. [ABSTRACT FROM AUTHOR]

• Flexible solid-state cells are developed with an in situ integration strategy. • A 20-µm-thick hybrid polymer/ceramic/ionic liquid electrolyte is prepared. • Stable interfaces are built, keeping intimate contact and reducing resistance. • The Li 4 Ti 5 O 12 /LiNi 0.8 Co 0.1 Mn 0.1 O 2 cell exhibits long cycling life at 30 °C. • The use of Si-based anode achieves 489.6 Wh kg−1 energy density at material's level. Flexible solid-state batteries (FSSBs) are indispensable energy storage devices to fulfil the energy and safety requirements for future flexible applications. The bottlenecks of FSSBs are how to realize high energy density with competent ionic conductivity for room-temperature (RT) flexible applications. Here, the first fabrication of RT FSSB with high energy density is reported, which is realized by in situ integration of a 20-µm-thick hybrid polymer/ceramic/ionic liquid solid-state electrolyte (SSE) between the high energy combination of anode/cathode electrodes. The in situ electrode/electrolyte interfacial integration strategy provides an ultrathin SSE layer, ultralow resistance and superior flexibility, and the SSE guarantees both high ionic conductivity and good compatibility with high-energy cathode LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811). The fabricated Li 4 Ti 5 O 12 /NCM811 FSSB delivers super-low resistance approaching conventional liquid cells and excellent cycling stability up to 600 cycles at RT. The extension of anode to SiO x @graphite leads to a high theoretical energy density of 489.6 Wh kg−1 at material's level, times higher than current options. In addition, the RT FSSB shows great flexibility, indicating a high performance application in future flexible electronics. [ABSTRACT FROM AUTHOR]

Layered Li-rich oxides (LLROs) attract much attention due to their high capacities. However, the electrolyte decomposition and interfacial reactions especially driven by the catalysis effect of high-valance transition metal ions under high voltage cause severe performance recession, hindering their practical applications. Lithium fluoride (LiF) is an effective component in both cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI) films. In this work, lithium 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide (LiHFDF) is employed as a novel electrolyte additive for generating LiF-abundant interphase on LLRO. With the addition of LiHFDF, the capacity retention and Coulombic efficiency of the LLRO are improved noticeably. In addition, the interfacial side reactions and voltage decay issues are mitigated. Transmission electron microscopy and X-ray photoelectron spectroscopy measurements confirm that a compact and thin CEI film with more LiF is formed on the cathode surface for the cell using LiHFDF, which is beneficial for the enhancement of the electrochemical performance. Moreover, differential scanning calorimetry (DSC) investigations reveal that the LLRO electrode with LiHFDF has improved safety compared to that with the blank electrolyte. This work provides an effective LiF-generating electrolyte additive for high-voltage LLROs, which is believed to be positive for other high-voltage cathode materials. • LiHFDF is employed as a novel electrolyte additive for LLROs. • LiHFDF is beneficial for generating LiF-abundant interphase. • The interphase improves the electrochemical performance of LLROs. • The interphase also enhances the safety character of LLROs. [ABSTRACT FROM AUTHOR]

High-performance electrode materials with intelligent design hold the promise for the development of lithium ion batteries regarding high energy density and long cycling life. Herein, we report an artificial solid electrolyte interphase (SEI) modified porous SiO x anode (P-SiO x) prepared by a facile in-situ polymerization of tannin (PTN) under alkaline condition, forming an elastic polymer layer surrounding P-SiO x particles. The as-prepared P-SiO x @PTN composite demonstrates higher initial Coulombic efficiency (ICE) and stronger mechanical property than the P-SiO x. Consequently, the outer elastic and electric buffer layer ensures the composite showing a high reversible capacity of 1616 mAh g−1 at 0.1 C and exceptional long-term cycling performance. Moreover, when coupled with LiNi 0.8 Mn 0.1 Co 0.1 O 2 cathode, high reversible capacity (123 mAh g−1) and good capacity retention (83 mAh g−1 after 300 cycles) at 0.5 C are achieved. This facile method constructing the artificial solid electrolyte interphase with enhanced mechanical and electrochemical properties by the in-situ PTN is of great promise for Si-based anode materials. Unlabelled Image • An artificial solid electrolyte interphase modified SiO x composite is prepared. • The artificial layer ensures the structure stability of the SiO x composite. • The as-prepared SiO x composite exhibits excellent electrochemical performance. [ABSTRACT FROM AUTHOR]