One article to understand the technical route of positive and negative electrode materials for solid-state batteries

2024-03-12 09:10 · Lithium Battery Encyclopedia

Solid-state batteries are currently one of the most active research directions in the field of secondary batteries. Theoretically, the energy density of all-solid-state lithium-ion batteries can reach 900Wh/kg. In terms of safety, due to the high elastic modulus of the solid electrolyte in solid-state batteries, it can effectively inhibit the growth of lithium dendrites and improve battery safety performance.

Schematic diagram of the internal structure of liquid/solid-state batteries

It is well known that solid electrolytes by themselves cannot increase energy density . However, compared with electrolytes, solid electrolytes are more stable, safer, and have a wide electrochemical window (above 5V). Therefore, they can be compatible with positive and negative electrodes with high specific capacities, such as high-voltage positive electrodes, lithium-rich bases, silicon negative electrodes, and lithium-ion negative electrodes. Materials such as metal negative electrodes can greatly increase the energy density of batteries. From the perspective of the battery structure: the solid electrolyte combines the separator function of the electrolyte into one, greatly reducing the distance between the positive and negative electrodes, thereby reducing the thickness of the battery, thereby increasing the volume energy density of the cell; in addition, the electrolyte of traditional liquid lithium-ion batteries has the ability to flow The internal stacked series connection is prone to short circuit, causing self-discharge and heat generation. Solid electrolytes are not fluid, and solid-state batteries can realize series connection and boost voltage inside the cells, which can reduce the packaging cost of the cells and increase the volumetric energy density.

Schematic diagram of liquid/solid battery structure

The solid-state battery cathode system is relatively complete, and high specific energy is the main line of gradual innovation.

The current cathode material system can continue to be used, and high-voltage cathode materials can be used to achieve higher energy density in the future: when the voltage exceeds 4V, the traditional organic electrolyte begins to decompose, making it difficult to increase the upper limit of the battery voltage, and the interface reaction between the solid electrolyte and the electrode material There are almost no side reactions of solid electrolyte decomposition and can withstand higher voltages (5V). Therefore, cathode materials with higher voltage platforms can be used in solid-state batteries to obtain higher energy density by increasing the operating voltage. By incorporating a small amount of transition metal ions into LiMn2O4, the LiNi0.5Mn1.5O4 formed has a theoretical capacity of 147mAh/g and a voltage platform of 4.7V; the lithium-rich manganese-based cathode is composed of layered Li2MnO3 and layered LiMO2 (M=Ni, Solid solution formed by Co, Mn or any combination) in different proportions, the theoretical gram capacity can reach 320mAh/g, the voltage platform is 3.7V-4.6V, the gram capacity and voltage platform are significantly higher than traditional medium and low nickel ternary and iron phosphate Lithium cathode material is an ideal cathode material for all-solid-state batteries.