Controlling Ni2+ from the Surface to the Bulk by a New Cathode Electrolyte Interphase Formation on a Ni-Rich Layered Cathode in High-Safe and High-Energy-Density Lithium-Ion Batteries

Tuning the Cathode-Electrolyte Interphase Chemistry with Multifunctional Additive for High-Voltage Li-Ion Batteries

The utilization of layered oxides as cathode materials has significantly contributed to the advancement of the lithium-ion batteries (LIBs) with high energy density and reliability. However, the structural and interfacial instability triggered by side reactions when charged to high voltage has plagued their practical applications. Here, this work reports a novel multifunctional additive, id est, 7-Anilino-3-diethylamino-6-methyl fluoran (ADMF), which exhibits unique characteristics such as preferential adsorption, oxygen scavenging, and electropolymerization protection for high-voltage cathodes. The ADMF demonstrates the capability to ameliorate the growth of cathode-electrolyte interphase (CEI), effectively diminishing the dissolution of transition metal (TM) ions, reducing the interface impedance, and facilitating the Li+ transport. As a result, ADMF additive with side reaction-blocking ability significantly enhances the cycling stability of MCMB||NCM811 full-cells at 4.4 V and MCMB||LCO full-cells at 4.55 V, as evidenced by the 80% retention over 600 cycles and 87% retention after 750 cycles, respectively. These findings highlight the potential of the additive design strategy to modulate the CEI chemistry, representing a new paradigm with profound implications for the development of next-generation high-voltage LIBs.

Having Your Cake and Eating It Too: Electrode Processing Approach Improves Safety and Electrochemical Performance of Lithium-Ion Batteries

A layered Li[Ni_xCo_yMn_1-x-y]O₂ (NCM)-based cathode is preferred for its high theoretical specific capacity. However, the two main issues that limit its practical application are severe safety issues and excessive capacity decay. A new electrode processing approach is proposed to synergistically enhance the electrochemical and safety performance. The polyimide's (PI) precursor is spin-coated on the LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) electrode sheet, and the homogeneous sulfonated PI layer is in situ produced by thermal imidization reaction. The PI-spin coated (PSC) layer provides improvements in capacity retention (86.47% vs 53.77% after 150 cycles at 1 C) and rate performance (99.21% enhancement at 5 C) as demonstrated by the NCM523-PSC||Li half-cell. The NCM523-PSC||graphite pouch full cell proves enhanced capacity retention (76.62% vs 58.58% after 500 cycles at 0.5 C) as well. The thermal safety of the NCM523-PSC cathode-based pouch cell is also significantly improved, with the critical temperature of thermal safety T₁ (the beginning temperature of obvious self-heating temperature) and thermal runaway temperature T₂ increased by 60.18 and 44.59 °C, respectively. Mechanistic studies show that the PSC layer has multiple effects as a passivation layer such as isolation of electrode-electrolyte contact, oxygen release suppression, solvation structure tuning, and the decomposition of carbonate solvents as well as LiPF₆ inhibition. This work provides a new path for a cost-effective and scalable design of electrode decoration with synergistic safety-electrochemical kinetics enhancement.

In Situ Co-O Bond Reinforcement of the Artificial Cathode Electrolyte Interphase in Highly Delithiated LiCoO2 for High-Energy-Density Applications

Highly delithiated LiCoO₂ has high specific capacity (>200 mAh g^-1); however, its degradation behavior causes it to have poor electrochemical performance and thermal instability. The degradation of highly delithiated LiCoO₂ is mainly induced by oxygen vacancy migration and weakening of oxygen-related interactions, which result in pitting corrosion and fault formation on the surface. In this research, a coupling agent, namely, 3-aminopropyltriethoxysilane (APTES), was grafted onto the surface of LiCoO₂ to form a cross-linking structure. Through the aza-Michael addition reaction, an oligomer formed from barbituric acid and bisphenol a diglycidyl ether diacrylate were reacted with the cross-linking APTES to form an artificial cathode electrolyte interphase (ACEI). The highly delithiated LiCoO₂ containing the ACEI had considerably less degradation on the surface of the bulk material caused by oxygen release. The formation of the O1 phase was prevented in high delithiation and high-temperature operations. This research revealed that the ACEI reinforced the Co-O bond, which is crucial in preventing gas evolution and O1 phase formation. In addition, the ACEI prevents direct contact between the electrolyte and highly active surface of LiCoO₂, thereby preventing the formation of a thick and high impedance traditional cathode electrolyte interphase. According to the present results, highly delithiated LiCoO₂ containing the ACEI exhibited outstanding cycle retention and capacity at 55 °C as well as low heat capacity release in the fully delithiated state. The ACEI considerably protected and maintained the electrochemical performance of highly delithiated LiCoO₂, which is suitable for high-energy-density applications, such as electric vehicles and power tools.