Maintaining structure and voltage stability of Li-rich cathode materials by green water-soluble binders containing Na⁺ ions

As high-capacity cathode materials for lithium-ion batteries, Li-rich materials still suffer from structure transformation during cycling, resulting in serious voltage fading. The improved properties achieved by traditional modification methods, such as surface coating and ion doping, are unsatisfactory. Here, two water-soluble binders, sodium carboxymethyl cellulose and sodium alginate, are employed to prepare electrodes in order to alleviate voltage fading of both Li_1.2Ni_0.2Mn_0.6O₂ and Li_1.2Co_0.13Ni_0.13Mn_0.54O₂ during cycling. Besides the environmental friendliness, these two water-soluble binders have better bonding ability with active particles and conductive agent than that of conventional PVDF binder. Moreover, Na⁺ ions in water-soluble binders are speculated to occupy lithium vacancies in crystal structure during cycling and play an important role as a pillar in lithium layer, leading to good structure stability of Li-rich materials. Accordingly, the electrodes based on water-soluble binders exhibit improved electrochemical performances, including high reversible discharge specific capacity, excellent cycling stability, and good rate capability. Importantly, voltage fading as a stubborn issue of Li-rich materials is significantly alleviated by using these water-soluble binders to prepare electrodes. Exploring suitable binders for specific electrode materials is considered as an effective strategy to improve electrochemical properties of electrode materials for lithium-ion batteries.