By breaking through the energy density limits step-by-step, the use of lithium cobalt oxide-based Li-ion batteries (LCO-based LIBs) has led to the unprecedented success of consumer electronics over the past 27 years. Recently, strong demands for the quick renewal of the properties of electronic products every so often have resulted in smarter, larger screened, more lightweight devices with longer standby times that have pushed the energy density of LCO-based LIBs nearly to their limit. As a result, with the aim of achieving a higher energy density and lifting the upper cut-off voltage of LCO above 4.45 V (vs. Li/Li⁺), the development of LCO-based all-solid-state lithium batteries (ASSLBs) with a Li metal anode and LCO-based full cells with high-performance anodes have become urgent scientific and technological requirements. This review summarizes the key challenges of synthesizing LCO-based LBs with a higher energy density from the perspectives of structure and interface stability, and gives an account of effective modification strategies in view of the electrodes, liquid electrolytes, binders, separators, solid electrolytes and LCO-based full cells. The improvement mechanisms of these modification strategies and the controversy over them are also analyzed critically. Moreover, some perspectives regarding the remaining challenges for LCO-based LBs towards a higher energy density and possible future research focuses are also presented.

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.

Although the theoretical specific capacity of LiCoO₂ is as high as 274 mAh g⁻¹, the superior electrochemical performances of LiCoO₂ can be barely achieved due to the issues of severe structure destruction and LiCoO₂/electrolyte interface side reactions when the upper cutoff voltage exceeds 4.5 V. Here, a bifunctional self‐stabilized strategy involving Al+Ti bulk codoping and gradient surface Mg doping is first proposed to synchronously enhance the high‐voltage (4.6 V) performances of LiCoO₂. The comodified LiCoO₂ (CMLCO) shows an initial discharge capacity of 224.9 mAh g⁻¹ and 78% capacity retention after 200 cycles between 3.0 and 4.6 V. Excitingly, the CMLCO also exhibits a specific capacity of up to 142 mAh g⁻¹ even at 10 C. Moreover, the long‐term cyclability of CMLCO/mesocarbon microbeads full cells is also enhanced significantly even at high temperature of 60 °C. The synergistic effects of this bifunctional self‐stabilized strategy on structural reversibility and interfacial stability are demonstrated by investigating the phase transitions and interface characteristics of cycled LiCoO₂. This work will be a milestone breakthrough in the development of high‐voltage LiCoO₂. It will also present an instructive contribution for resolving the big structural and interfacial challenges in other high‐energy‐density rechargeable batteries.

This review focuses on the chemical thermodynamics and reaction kinetics of intrinsic and anionic redox-mediated oxygen vacancies in oxide cathodes.