High nickel content in LiNi_xCo_yMn_zO₂ (NCM, x ≥ 0.8, x + y + z = 1) layered cathode material allows high specific energy density in lithium-ion batteries (LIBs). However, Ni-rich NCM cathodes suffer from performance degradation, mechanical and structural instability upon prolonged cell cycling. Although the use of single-crystal Ni-rich NCM can mitigate these drawbacks, the ion-diffusion in large single-crystal particles hamper its rate capability. Herein, we report a strategy to construct an in situ Li_1.4Y_0.4Ti_1.6(PO₄)₃ (LYTP) ion/electron conductive network which interconnects single-crystal LiNi_0.88Co_0.09Mn_0.03O₂ (SC-NCM88) particles. The LYTP network facilitates the lithium-ion transport between SC-NCM88 particles, mitigates mechanical instability and prevents detrimental crystalline phase transformation. When used in combination with a Li metal anode, the LYTP-containing SC-NCM88-based cathode enables a coin cell capacity of 130 mAh g⁻¹ after 500 cycles at 5 C rate in the 2.75-4.4 V range at 25 °C. Tests in Li-ion pouch cell configuration (i.e., graphite used as negative electrode active material) demonstrate capacity retention of 85% after 1000 cycles at 0.5 C in the 2.75-4.4 V range at 25 °C for the LYTP-containing SC-NCM88-based positive electrode.

Solid-state Li batteries are promising energy storage devices owing to their high safety and high theoretical energy density. However, the serious interfacial reaction between solid state electrolytes and cathodes deteriorates the battery performance, impeding the realization of long-term cyclability. The buried nature of the interphase layer presents a significant challenge in achieving a comprehensive understanding of the underlying interfacial reaction mechanisms. Herein, we systematically explore the interfacial reaction evolutions and interphase compositions and electronic properties between the popular oxide cathodes and sulfide solid electrolytes (SSEs). This includes analysis of the chemical and electrochemical reactions between cathodes/coatings and SSEs, as well as the electrochemical self-decomposition of SSEs by thermodynamic phase equilibrium analysis. We disclose that the driving force of the electrochemical reaction at the chemical potential of μ_Li is much stronger than that of the chemical reaction, which dominates the interfacial reaction. Preventing the formation of an electronically conductive interphase is crucial in inhibiting the continuous interfacial degradation during long-term cycling, which can be achieved through the optimized combination of cathodes and SSEs, as well as the introduction of functional coatings between them. Based on these findings, the percentage of molar fraction (f) of electronically conductive species in the formed interphase is proposed as a key factor for indicating the interfacial stability for the first time. Furthermore, we propose a specific high-throughput screening scheme to filter the functional coating materials by comprehensively evaluating their functionality. The tiered screening identifies 48 coating materials with optimal properties. The work highlights the significant roles of rational coupling of the cathodes and SSEs, and optimizing interfacial coating materials for solid-state batteries. It opens new avenues for engineering an interphase with improved interfacial compatibility to realize long-term cyclability.

Lithium‐ion batteries based on single‐crystal LiNi_1−x−yCo_xMn_yO₂ (NCM, 1−x−y ≥ 0.6) cathode materials are gaining increasing attention due to their improved structural stability resulting in superior cycle life compared to batteries based on polycrystalline NCM. However, an in‐depth understanding of the less pronounced degradation mechanism of single‐crystal NCM is still lacking. Here, a detailed postmortem study is presented, comparing pouch cells with single‐crystal versus polycrystalline LiNi_0.60Co_0.20Mn_0.20O₂ (NCM622) cathodes after 1375 dis‐/charge cycles against graphite anodes. The thickness of the cation‐disordered layer forming in the near‐surface region of the cathode particles does not differ significantly between single‐crystal and polycrystalline particles, while cracking is pronounced for polycrystalline particles, but practically absent for single‐crystal particles. Transition metal dissolution as quantified by time‐of‐flight mass spectrometry on the surface of the cycled graphite anode is much reduced for single‐crystal NCM622. Similarly, CO₂ gas evolution during the first two cycles as quantified by electrochemical mass spectrometry is much reduced for single‐crystal NCM622. Benefitting from these advantages, graphite/single‐crystal NMC622 pouch cells are demonstrated with a cathode areal capacity of 6 mAh cm⁻² with an excellent capacity retention of 83% after 3000 cycles to 4.2 V, emphasizing the potential of single‐crystalline NCM622 as cathode material for next‐generation lithium‐ion batteries.

Large-scale molecular dynamics simulations reveal the formation mechanism and structure of the solid electrolyte interphase between lithium metal and β-Li₃PS₄ in all-solid-state batteries.