Longlong Wang

Sulfide solid electrolytes have high ionic conductivities necessary to achieve high-rate solid-state cathodes at room temperature and low pressure. Cathode active materials generally require coatings to avoid deleterious oxidative decomposition reactions with the electrolyte. Coatings add cost and complexity to the manufacture. Here we decouple the effect of double and triple phase boundaries on the decomposition in the thick (i.e., ∼110 μm) uncoated solid state cathode. We show that more severe oxidative decomposition of solid electrolytes occurs when the cathode active materials, carbon, and the solid electrolyte coexist, highlighting the importance of the triple phase boundary concerning the decomposition. By regulating the electronic pathways at the triple phase boundary, a thick uncoated electrode at 1 mA cm^–2 and 2 MPa stack pressure, delivers an initial areal capacity of ∼4.6 mAh cm^–2 at 30 °C and ∼85% capacity retention after 500 cycles.

Hybrid electrolytes with an argyrodite separator and liquid catholyte show promise for Li–S batteries. We show liquid electrolyte choice determines solid–liquid interphase properties, with significant implications for battery performance.

Efforts to avoid dendrites by increasing the interfacial surface area to lower local current densities are limited by significant local pressure accumulation associated with the topography of any surface contouring.

All-solid-state lithium batteries (ASSLBs) have been regarded as one of the most promising next-generation batteries in terms of their superior safety and great potential to meet the requirements of high energy and power density.¹ However, the performance of ASSLBs based on even state-of-the-art solid electrolytes (SEs) with a high room-temperature ion conductivity of 10⁻² S·cm⁻¹ is still inferior to that of commercially available LIBs, because fast solid electrode/electrolyte interfacial lithium-ion transport remains a vital challenge in ASSLBs.² The sluggish lithium-ion transport across the solid electrode/electrolyte interface mainly results from the electro-chemo-mechanical degradation, such as the space charge layer (SCL), interface reaction generating ionically resistive products, and poor physical contact.^3,4 On the cathode side, coating high-voltage cathodes with chemically compatible and stable buffering layers with high ionic conductivity but low electronic conductivity has been widely confirmed to be an effective approach to overcome these problems.However, a mechanistic understanding of the coating functionality remains unresolved, and there is still much room for improvement regarding the methodology and associated material properties.⁵ Here, from electro-chemo-mechanical perspectives, we have fully studied the improvement mechanism of cathode interface engineering for ASSLBs based on the complementary analyses including calculations (e.g., first-principles, finite element methods), in-situ (e.g., differential phase contrast scanning transmission electron microscopy (DPC-STEM), Raman, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT)) and ex-situ (X-ray absorption spectra (XAS), X-ray photoelectron spectroscopy (XPS), focused-ion beam scanning electron microscopy (FIB-SEM)) characterizations. We find that discontinuous ferroelectric BaTiO₃ coating can effectively suppress the SCL formation and lead to fast continuous interfacial lithium-ion conduction pathways, thus significantly improving the interfacial migration kinetics between cathode materials and the sulfide SEs.⁶ The bidirectionally compatible NASICON-type Li_xZr₂(PO₄)₃ (LZPO) buffering layer enables the high-voltage cathode interface (4.5 V LiCoO₂/Li₆PS₅Cl) with high chemical/electrochemical stability and fast Li-ion transport dynamics.⁷ Additionally, the high Young’s modulus of the coating layer (e.g., LZPO) can remarkably decrease stress inside cathodes and prevent cathode/SE interface separation, which is beneficial to mitigate microcracks in cathodes and cathode/SE interface contact loss, respectively.⁸ We believe these findings will help advance the fundamental scientific understanding of the coating functionality and the interfacial lithium-ion transport mechanism in ASSLBs, thus shed light on rational electrode/electrolyte interface design for high-rate performance ASSLBs. References Janek, J. & Zeier, W. G. A solid future for battery development. Nat. Energy 1, 16141 (2016). Janek, J. & Zeier, W. G. Challenges in speeding up solid-state battery development. Nat. Energy, doi:10.1038/s41560-023-01208-9 (2023). Banerjee, A., Wang, X., Fang, C., Wu, E. A. & Meng, Y. S. Interfaces and Interphases in All-Solid-State Batteries with Inorganic Solid Electrolytes. Chem. Rev. 120, 6878–6933 (2020). Chen, R., Li, Q., Yu, X., Chen, L. & Li, H. Approaching Practically Accessible Solid-State Batteries: Stability Issues Related to Solid Electrolytes and Interfaces. Chem. Rev. 120, 6820–6877 (2020). Culver, S. P., Koerver, R., Zeier, W. G. & Janek, J. On the functionality of coatings for cathode active materials in thiophosphate-based all-solid-state batteries. Adv. Energy Mater. 9, 1900626 (2019). Wang, L. et al. In-situ visualization of the space-charge-layer effect on interfacial lithium-ion transport in all-solid-state batteries. Nat. Commun. 11, 5889 (2020). Wang, L. et al. Bidirectionally compatible buffering layer enables highly stable and conductive interface for 4.5 V sulfide-based all-solid-state lithium batteries. Adv. Energy Mater. 11, 2100881 (2021). Sun, X. et al. A Bifunctional Chemomechanics Strategy To Suppress Electrochemo-Mechanical Failure of Ni-Rich Cathodes for All-Solid-State Lithium Batteries. ACS Appl. Mater. Interfaces 14, 17674–17681 (2022).

A critical current challenge in the development of all-solid-state lithium batteries (ASSLBs) is reducing the cost of fabrication without compromising the performance. Here we report a sulfide ASSLB based on a high-energy, Co-free LiNiO₂ cathode with a robust outside-in structure. This promising cathode is enabled by the high-pressure O₂ synthesis and subsequent atomic layer deposition of a unique ultrathin Li_xAl_yZn_zO_δ protective layer comprising a Li_xAl_yZn_zO_δ surface coating region and an Al and Zn near-surface doping region. This high-quality artificial interphase enhances the structural stability and interfacial dynamics of the cathode as it mitigates the contact loss and continuous side reactions at the cathode/solid electrolyte interface. As a result, our ASSLBs exhibit a high areal capacity (4.65 mAh cm⁻²), a high specific cathode capacity (203 mAh g⁻¹), superior cycling stability (92% capacity retention after 200 cycles) and a good rate capability (93 mAh g⁻¹ at 2C). This work also offers mechanistic insights into how to break through the limitation of using expensive cathodes (for example, Co-based) and coatings (for example, Nb-, Ta-, La- or Zr-based) while still achieving a high-energy ASSLB performance.

Electrochemo-mechanical failure of Ni-rich cathodes leads to rapid performance degradation, and thus hinders their practical implementation in all-solid-state lithium batteries (ASSLBs). To solve this problem, herein, we propose a bifunctional chemomechanics strategy by protecting polycrystalline LiNi_0.6Co_0.2Mn_0.2O₂ (NCM) cathodes using a high-mechanical-strength fast ionic conductor LiZr₂(PO₄)₃ (LZP) coating layer. The coating layer’s synergistic effect between mechanical strength and electrochemical stability is studied in Li₆PS₅Cl (LPSCl)-based ASSLBs for the first time. Using finite element method (FEM) simulations and various characterization techniques, we demonstrate that the robust and stable LZP (Young’s modulus 140.7 GPa, electrochemical stability window >5 V) coating layer mitigates the volume change and particle disintegration of polycrystalline NCM and electrochemical decomposition of LPSCl on the LPSCl/NCM interface. As a result, the LZP-modified ASSLBs display remarkably improved reversible capacity, cycle life, and rate performance. The synergy of mechanical and electrochemical properties of the coating layer will provide valuable guidance for the development of high-energy-density ASSLBs.

Owing to its high energy density, LiNi_0.8Co_0.1Mn_0.1O₂ (NMC811) is a cathode material of prime interest for electric vehicle battery manufacturers. However, NMC811 suffers from several irreversible parasitic reactions that lead to severe capacity fading and impedance buildup during prolonged cycling. Thin surface protection films coated on the cathode material mitigate degradative chemomechanical reactions at the electrode–electrolyte interphase, which helps to increase cycling stability. However, these coatings may impede the diffusion of lithium ions, and therefore, limit the performance of the cathode material at a high C-rate. Herein, we report on the synthesis of zirconium phosphate (Zr_xPO_y) and lithium-containing zirconium phosphate (Li_xZr_yPO_z) coatings as artificial cathode–electrolyte interphases (ACEIs) on NMC811 using the atomic layer deposition technique. Upon prolonged cycling, the Zr_xPO_y- and Li_xZr_yPO_z-coated NMC811 samples show 36.4 and 49.4% enhanced capacity retention, respectively, compared with the uncoated NMC811. Moreover, the addition of Li ions to the Li_xZr_yPO_z coating enhances the rate performance and initial discharge capacity in comparison to the Zr_xPO_y-coated and uncoated samples. Using online electrochemical mass spectroscopy, we show that the coated ACEIs largely suppress the degradative parasitic side reactions observed with the uncoated NMC811 sample. Our study demonstrates that providing extra lithium to the ACEI layer improves the cycling stability of the NMC811 cathode material without sacrificing its rate capability performance.

The space charge layer (SCL) is generally considered one of the origins of the sluggish interfacial lithium-ion transport in all-solid-state lithium-ion batteries (ASSLIBs). However, in-situ visualization of the SCL effect on the interfacial lithium-ion transport in sulfide-based ASSLIBs is still a great challenge. Here, we directly observe the electrode/electrolyte interface lithium-ion accumulation resulting from the SCL by investigating the net-charge-density distribution across the high-voltage LiCoO₂/argyrodite Li₆PS₅Cl interface using the in-situ differential phase contrast scanning transmission electron microscopy (DPC-STEM) technique. Moreover, we further demonstrate a built-in electric field and chemical potential coupling strategy to reduce the SCL formation and boost lithium-ion transport across the electrode/electrolyte interface by the in-situ DPC-STEM technique and finite element method simulations. Our findings will strikingly advance the fundamental scientific understanding of the SCL mechanism in ASSLIBs and shed light on rational electrode/electrolyte interface design for high-rate performance ASSLIBs.