Engineered polycrystalline electrodes are critical to the cycling stability and safety of lithium-ion batteries, yet it is challenging to construct high-quality coatings at both the primary-and secondaryparticle levels. Here, we present a room-temperature synthesis route to achieve full surface coverage of secondary particles and facile infusion into grain boundaries, thus offering a complete "coatingplus-infusion" strategy. Cobalt boride metallic glass is successfully applied to Ni-rich layered cathode LiNi 0.8 Co 0.1 Mn 0.1 O 2 . It dramatically improves the rate capability and cycling stability, including under high-discharge-rate and elevated-temperature conditions and in pouch full cells.The superior performance originates from simultaneous suppression of microstructural degradation of intergranular cracking and side reactions with electrolyte. Atomistic simulations identified the critical role of strong selective interfacial bonding, which offers not only a large chemical driving force to ensure uniform reactive wetting and facile infusion but also lowered the surface/interface 2 oxygen activity, contributing to the exceptional mechanical and electrochemical stabilities of the infused electrode.

Lithium-excess 3d-transition-metal layered oxides (Li1+xNiyCozMn1−x−y−zO2, >250 mAh g−1) suffer from severe voltage decay upon cycling, which decreases energy density and hinders further research and development. Nevertheless, the lack of understanding on chemical and structural uniqueness of the material prevents the interpretation of internal degradation chemistry. Here, we discover a fundamental reason of the voltage decay phenomenon by comparing ordered and cation-disordered materials with a combination of X-ray absorption spectroscopy and transmission electron microscopy studies. The cation arrangement determines the transition metal-oxygen covalency and structural reversibility related to voltage decay. The identification of structural arrangement with de-lithiated oxygen-centred octahedron and interactions between octahedrons affecting the oxygen stability and transition metal mobility of layered oxide provides the insight into the degradation chemistry of cathode materials and a way to develop high-energy density electrodes.

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A practical solution is presented to increase the stability of 4.45 V LiCoO 2 via high-temperature Ni doping, without adding any extra synthesis step or cost. How a putative uniform bulk doping with highly soluble elements can profoundly modify the surface chemistry and structural stability is identified from systematic chemical and microstructural analyses. This modification has an electronic origin, where surface-oxygen-loss induced Co reduction that favors the tetrahedral site and causes damaging spinel phase formation is replaced by Ni reduction that favors octahedral site and creates a better cation-mixed structure. The findings of this study point to previously unspecified surface effects on the electrochemical performance of battery electrode materials hidden behind an extensively practiced bulk doping strategy. The new understanding of complex surface chemistry is expected to help develop higherenergy-density cathode materials for rechargeable batteries.

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.

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along the grain boundaries. [12][13][14][15] Consequently, such structural instability causes rapid capacity fading and poor electrochemical performance, which are ascribed to the deteriorated ionic and electronic conduction. To date, many surface treatment and morphology control technologies have been suggested to prevent capacity fading and structure degradation during cycling. [3] For the surface treatment of nickel-based layered cathodes, this concept is considered as a very simple and viable way by introducing additional layers consisting of polymer, [16] metal phosphate, [17,18] metal fluoride, [19,20] metal oxide, [21,22] or core shell [23][24][25] on the surface of the secondary particle clusters. The point that is often overlooked, however, is that these approaches do not fully prevent the fundamental issues related to the grain boundaries among the primary particles. In this context, a novel concept of full concentration-gradient of manganeserich phase with long rod-shaped primary particles was reported and demon strated good structural stability. [26][27][28][29][30] More recently, Cho and co-workers introduced two approaches for the grain boundary coating including the nanoscale surface treatment by cobalt-rich cation mixing layer [31] and spinel-like Li x CoO 2 layer as a glue-nanofiller [32] for highly stable active materials, where an improved structural and thermal stability was achieved by suppressing the phase transition from layered to rock-salt phase of primary particles. However, these kinds of surface treatment methods accompanied a multistep coprecipitation process [29,30] or were carried out after coprecipitation process of active materials by using additional chemicals for surface coatings, [31][32][33] which can cause the increase of the process time and capital cost.Herein, we report a highly stable LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathode with a TM concentration gradient in primary particles and inner pores in secondary particles via a simple, one-step coprecipitation method by exploiting polymeric-beads as a sacrificial template without any surface coating reagents. The prepared sample retains the self-induced TM concentration gradient with reduced nickel oxidation state in the primary particles, which significantly improved the structural stability by suppressing the evolution of microcracks in cathode particles at a high voltage cutoff of 4.45 V and even at a high temperature of 60 °C. Additionally, the internal pores in the secondary particles successfully provided a buffer effect against the volume change of the primary particles.The synthesis process for polystyrene beads (PSBs) incorporated LiNi 0.6 Co 0.2 Mn 0.2 O 2 , denoted as a PSB-NCM, is simple and highly scalable. Briefly, the cathode precursor, PSB-Ni 0.6 Co 0.2 Mn 0.2 (OH) 2 , was synthesized by the coprecipitation To meet the demand of electric vehicles and electrical energy storage systems, lithium-ion batteries with high energy density, high rate capability, and thermal stability have been required. [1][2][3] Among the man...

Li‐ and Mn‐rich layered oxides (LMRs) have emerged as practically feasible cathode materials for high‐energy‐density Li‐ion batteries due to their extra anionic redox behavior and market competitiveness. However, sluggish kinetics regions (<3.5 V vs Li/Li+) associated with anionic redox chemistry engender LMRs with chemical irreversibility (first‐cycle irreversibility, poor rate properties, voltage fading), which limits their practical use. Herein, the structural origin of this chemical irreversibility is revealed through a comparative study involving Li1.15Mn0.51Co0.17Ni0.17O2 with relatively localized and delocalized excess‐Li in its lattice system. Operando fine‐interval X‐ray absorption spectroscopy is used to simultaneously observe the interplay between transition‐metal–oxygen (TM‐O) redox chemistry and TM migration behavior in real time. Density functional theory calculations show that excess‐Li localization in the LMR structure attenuates TM‐O covalency and stability, leading to overall chemical irreversibility. Hence, the delocalized excess‐Li system is proposed as an alternative design for practically feasible LMR cathodes with restrained TM migration and sustainable O‐redox chemistry.