Electrode Surface Modification to Improve Lithium-Ion Battery Performance Our expertise

In industrial LIBs, there are several lithium-transition-metal-oxide- based cathode materials such as lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickel manganese cobalt oxide (LiNi1/3Mn1/3Co1/3O2), lithium iron phosphate (LiFePO4), and lithium nickel cobalt aluminum (LiNi0·8Co0·15O2) are being used.

These cathode materials have several drawbacks such as low conductivity and the fast capacity fading upon repeated charge-discharge cycles. To overcome these challenges of the existing cathode materials, it has been reported that surface modification of the cathode materials is a cost-effective and reasonable technology to enhance their energy storage performances such as capacity retention, cyclability, and thermal stability.

Surface modification techniques such as doping, noble metal catalysts loading, loading of metal oxides, and formation of nanocomposites are being used by various researchers. Among these techniques, surface coating was found to be most effective because it improves not only capacity retention and rate capability but also the thermal stability of cathode materials for energy storage devices.

Presently, the structure of surface coating materials is of two types: first, coating of the cathode surface with a heterogeneous material of a few nanometers thickness, and second, coating the cathode surface with separate materials in different layers to form a composite.

The surface coating also provides safety layers to reduce the direct contact of the active material with the electrolyte. Carbon, metal oxides, metal aluminates, metal carbonates, metal hydroxides, metal fluorides, metal oxyfluorides, metal phosphates, and Li2O.2B2O3 glass have been explored as coating materials.

Graphite, a commercial anode material used in LIBs, is still considered the most promising material because of its excellent cycle reversibility, stable cycle life, and superior electronic conductivity. Despite these advantages, due to its low theoretical capacity (~372 mAh g−1) and limited rate capability under fast charging conditions, graphite cannot meet the growing performance requirements of LIBs.

The slow kinetics of lithium intercalation at the graphite–electrolyte interface during rapid charging conditions can lead to an undesirable anode voltage drop below 0 V vs. Li/Li+, resulting in the formation of lithium plating on the graphite surface. This phenomenon can cause capacity decay, dendrite growth, short circuits, and even serious safety issues.

To overcome this challenge, various approaches have been proposed to develop high-power LIB anodes with improved interfacial kinetics. Among these approaches, surface modification using transition metal sulfides (TMDs) has emerged as an effective strategy to enhance the rate capability and cycle stability of graphite anodes. The resulting composite exhibits improved specific capacity, rate capability, and cycle stability compared to commercial graphite anodes.

The rate performance of electrodes after surface modification can be observed by studying the specific surface area and pore size. When there is an increase in specific surface area, the number of functional groups on the surface increase, and the proportion of active sites increase.

By offering abundant exposed active sites, it facilitates lithium diffusion, and the rate characteristics and specific capacity of LIBs are expected to improve. The specific surface area and pore structure can be derived from the adsorption and desorption isotherm measurements.