Boosting Reaction Homogeneity in High‐Energy Lithium‐Ion Battery Cathode Materials

Abstract

Conventional nickel‐rich cathode materials suffer from reaction heterogeneity during electrochemical cycling particularly at high temperature, because of their polycrystalline properties and secondary particle morphology. Despite intensive research on the morphological evolution of polycrystalline nickel‐rich materials, its practical investigation at the electrode and cell levels is still rarely discussed. Herein, an intrinsic limitation of polycrystalline nickel‐rich cathode materials in high‐energy full‐cells is discovered under industrial electrode‐fabrication conditions. Owing to their highly unstable chemo‐mechanical properties, even after the first cycle, nickel‐rich materials are degraded in the longitudinal direction of the high‐energy electrode. This inhomogeneous degradation behavior of nickel‐rich materials at the electrode level originates from the overutilization of active materials on the surface side, causing a severe non‐uniform potential distribution during long‐term cycling. In addition, this phenomenon continuously lowers the reversibility of lithium ions. Consequently, considering the degradation of polycrystalline nickel‐rich materials, this study suggests the adoption of a robust single‐crystalline LiNi0.8Co0.1Mn0.1O2 as a feasible alternative, to effectively suppress the localized overutilization of active materials. Such an adoption can stabilize the electrochemical performance of high‐energy lithium‐ion cells, in which superior capacity retention above ≈80% after 1000 cycles at 45 °C is demonstrated.

Single‐ or Poly‐Crystalline Ni‐Rich Layered Cathode, Sulfide or Halide Solid Electrolyte: Which Will be the Winners for All‐Solid‐State Batteries?

“…[18,37,38,52] Moreover, very recently, our group demonstrated that commercial-grade LiNi 0.80 Co 0.10 Mn 0.10 O 2 , consisting of randomly oriented grains, was susceptible to severe disintegration of the secondary particles even at the initial charge and discharge due to the anisotropic volumetric strains, which led to poor electrochemical performance of low ICE and degradation of cycling retention. [37] In this regard, recently emerging research directions for cathodes in advanced LIBs based on LEs, the development of cracking-free single-crystalline Ni-rich layered oxides, [30,[53][54][55][56][57][58] could be in the same vein for the development of practical ASLBs.The recent discovery of halide SEs (Li 3 YX 6 (X = Cl, Br)) with Li + conductivities of over 10 −4 S cm −1 has opened new opportunities due to their excellent electrochemical oxidation stability (>4 V vs Li/Li + ) and much better chemical stability (more oxygen-resistant and no H 2 S evolution), compared to sulfide SEs, as well as deformability. [59,60] By exploration of the Li 3 YX 6 analogs, highly Li + conductive halide SEs of Li 3 InCl 6 (1.5 mS cm −1 ), [61] Li 3 ErCl 6 (0.33 mS cm −1 ), [62] Li 3 ScCl 6 (3.0 mS cm −1 ), [63,64] and Li 3−x M 1−x Zr x Cl 6 (M = Y, Er, 1.4 mS cm −1 ), [65] Li 2+x Zr 1−x Fe x Cl 6 (max.…”

“…[18,37,38,52] Moreover, very recently, our group demonstrated that commercial-grade LiNi 0.80 Co 0.10 Mn 0.10 O 2 , consisting of randomly oriented grains, was susceptible to severe disintegration of the secondary particles even at the initial charge and discharge due to the anisotropic volumetric strains, which led to poor electrochemical performance of low ICE and degradation of cycling retention. [37] In this regard, recently emerging research directions for cathodes in advanced LIBs based on LEs, the development of cracking-free single-crystalline Ni-rich layered oxides, [30,[53][54][55][56][57][58] could be in the same vein for the development of practical ASLBs.…”

Surface Modification Engineering Enabling 4.6 V Single‐Crystalline Ni‐Rich Cathode with Superior Long‐Term Cyclability

“…The modification of LSTP enhanced the physical and chemical properties of the catheter material, indicating that under the conditions of electrode preparation, the SC-NCM@LSTP-1% material and therefore high mechanical strength can alleviate the volume change and structural collapse of the NCM material during the cycle, thereby obtaining a stable electrochemical capability. [25] Figure 6. Mechanical strength characterization of the SC-NCM and SC-NCM@LSTP-1%.…”

Insight into the Redox Reaction Heterogeneity within Secondary Particles of Nickel-Rich Layered Cathode Materials

“…(i) In terms of material preparation, due to the polycrystalline property and secondary-particle morphology, the inhomogeneous distribution of the transition mental elements (Ni, Co, Mn) within the materials would result in the heterogeneous redox reaction during the electrochemical charging/discharging process. − (ii) In the aspect of the Li + diffusion inhomogeneity, the solid-phase Li + diffusion in the cathode material is generally regarded as the rate-limiting step of the half-battery reaction. − In the process of energy storage, the difference in the diffusion rate of lithium ions will cause the heterogeneous reaction, especially under high-rate conditions. (iii) In the aspect of composite electrodes, owing to the complexity of the composition, the mismatch of the local ionic/electronic conductivity can cause the reaction heterogeneity between different particles at the electrode level. − The multiscale reaction heterogeneity would further lead to the inhomogeneous distribution of the state of charge (SOC) and stress at the electrode/particle level, thus accelerating the deterioration of the structure and electrochemical performances of the material. Therefore, it is urgent to systematically investigate the reaction heterogeneity in order to deeply understand the degradation mechanism of nickel-rich NCM materials and guide the modification research.…”

“…At present, researchers have made efforts to understand the reaction heterogeneity from multiscale perspectives. At the macro scale, Cha et al proposed that, due to the overutilization of the active materials at the surface side, the nickel-rich NCM particles suffer from reaction heterogeneity in the vertical direction of the electrode surface, causing the inhomogeneous distribution of SOC . By means of fast time-resolved in situ X-ray diffraction (XRD), Zhou et al reported the rate-dependent phase transition processes of LiNi 1/3 Co 1/3 Mn 1/3 O 2 during the fast charging processes and found that the intermediate phase between the H1 and H2 phases emerged at high rates (>10 C) and is closely related to the inhomogeneous distribution of SOC in materials .…”