An ever-increasing market for electric vehicles (EVs), electronic devices and others has brought tremendous attention on the need for high energy density batteries with reliable electrochemical performances. However, even the successfully commercialized lithium (Li)-ion batteries still face significant challenges with respect to cost and safety issues when they are used in EVs. From a cathode material point of view, layered transition-metal (TM) oxides, represented by LiMO 2 (M = Ni, Mn, Co, Al, etc.) and Li-/Mn-rich xLi 2 MnO 3 Á(1-x)LiMO 2 , have been considered as promising candidates because of their high theoretical capacity, high operating voltage, and low manufacturing cost. However, layered TM oxides still have not reached their full potential for EV applications due to their intrinsic stability issues during electrochemical processes. To address these problems, a variety of surface modification strategies have been pursued in the literature. Herein, we summarize the recent progresses on the enhanced stability of layered TM oxides cathode materials by different surface modification techniques, analyze the manufacturing process and cost of the surface modification methods, and finally propose future research directions in this area.

Cobalt (Co)-free ultrahigh-nickel (Ni) layered oxides exhibit dual competitive advantages in reducing the cathode cost and boosting the energy density, promising the sustainable development of batteries for electric vehicles. However, the increased Ni content and the resulting more highly oxidative Ni4+ potentially induce severe capacity fading due to the aggravated side reactions at the cathode surface, limiting the practical applications. Here, we evaluate the compatibility of two localized high-concentration electrolytes (LHCEs) with LiNi0.96Mg0.02Ti0.02O2 (NMT) cathode under a high charging voltage of 4.4 V in lithium-ion batteries. The LHCE with ethylene carbonate as additive enables the formation of effective interfacial layers on both the NMT cathode and graphite anode, realizing a capacity retention of 97.2% after 200 cycles and high reversible capacities of ∼180.2 and ∼185.8 mAh g–1 at 5C charge rate and 5C discharge rate, respectively, at 25 °C. This work provides a promising approach to enable Co-free ultrahigh-Ni layered oxides for practical applications.

The criticality of cobalt (Co) has been motivating the quest for Co-free positive electrode materials for building lithium (Li)-ion batteries (LIBs). However, the LIBs based on Co-free positive electrode materials usually suffer from relatively fast capacity decay when coupled with conventional LiPF 6 -organocarbonate electrolytes. To address this issue, a 1,2-dimethoxyethanebased localized high-concentration electrolyte (LHCE) was developed and evaluated in a Co-free Li-ion cell chemistry (graphite|| LiNi 0.96 Mg 0.02 Ti 0.02 O 2 ). Extraordinary capacity retentions were achieved with the LHCE in coin cells (95.3%), single-layer pouch cells (79.4%), and high-capacity loading double-layer pouch cells (70.9%) after being operated within the voltage range of 2.5−4.4 V for 500 charge/discharge cycles. The capacity retentions of counterpart cells using the LiPF 6 -based conventional electrolyte only reached 61.1, 57.2, and 59.8%, respectively. Mechanistic studies reveal that the superior electrode/electrolyte interphases formed by the LHCE and the intrinsic chemical stability of the LHCE account for the excellent electrochemical performance in the Co-free Liion cells.

high-voltage requirements. [1][2][3][4] However, the advancements of cathode active materials are overshadowed by the slow development of cathode binders, which should not be underestimated in terms of enabling practical cathode sheets. This issue becomes more stringent for the development of high-mass-loading cathode sheets, which have garnered considerable attention as a facile and scalable way to construct high-energy-density Li-ion batteries. [5][6][7] Major challenges facing the high-massloading cathode sheets include nonuniform electron/ion conduction networks in their through-thickness direction, [8][9][10][11][12] insufficient adhesion (between electrode active layers and current collectors) under electrolyte-soaked states, [13][14][15] and dissolution of transition metal (TM) ions from cathode active materials. [8,16,17] Notably, these challenges are closely dependent on cathode binders. Several previous studies on cathode binders have focused on the synthesis and engineering of new materials, with particular attention to replacing polyvinylidene fluoride (PVdF) binders that have been predominantly used in commercial cathodes. For example, gum materials [18,19] such as xanthan and guar gums with hydroxyl groups enhance the structural stability and electrochemical performance of overlithiated layered oxide (OLO) cathodes by chelating the dissolved TM ions. Carboxymethyl cellulose (CMC) exerted a strong binding force on OLO and mitigated the phase transition of OLO during cycling. [20,21] Owing to its hydroxyl groups, lignin enhanced the adhesion between LiNi 0.5 Mn 1.5 O 4 (LNMO) active materials and current collectors, and contributed to the formation of uniform cathode-electrolyte interphase (CEI). [22] In addition to these biomaterials, polyacrylic acid (PAA) [23] and Li-PAA [24] were explored as binders for the OLO and LNMO cathodes, which formed stable CEI layers and suppressed the dissolution of TM ions.However, these cathode binders were only suitable for aqueous slurry-based cathode fabrication processes due to their hydrophilic functional groups. More notably, these aqueous binders were not suitable for moisture-sensitive Ni-rich cathode active materials, which have gained considerable attention for high-energy-density Li-batteries used in long-range electric vehicles. The Ni-rich cathode active materials often undergo structural disruption when exposed to water molecules, [25] thus generating unwanted residual Li compounds such as LiOH and In contrast to noteworthy advancements in cathode active materials for lithium-ion batteries, the development of cathode binders has been relatively slow. This issue is more serious for high-mass-loading cathodes, which are preferentially used as a facile approach to enable high-energy-density Li-ion batteries. Here, amphiphilic bottlebrush polymers (BBPs) are designed as a new class of cathode binder material. Using poly (acrylic acid) (PAA) as a sidechain, BBPs are synthesized through ring-opening metathesis polymerization. The BBPs are amphiphilic in nature...

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