Currently, electric vehicles and energy storage systems mostly use lithium-ion batteries. Although they have high energy density and fast charging speeds, they also have safety issues. Therefore, the industry is actively developing solid-state batteries, hoping they can replace traditional lithium-ion batteries.
What is a solid-state battery?
Solid-state batteries are a type of battery technology. Unlike the commonly used lithium-ion and lithium-ion polymer batteries, solid-state batteries use solid electrodes and solid electrolytes.
In solid-state ionics, a solid-state battery is a type of battery that uses solid electrodes and a solid electrolyte. Solid-state batteries generally have lower power density but higher energy density. Due to their high power density, solid-state batteries are ideal for electric vehicles.
What is a lithium-ion battery?
A lithium-ion battery is a rechargeable battery that primarily functions by the movement of lithium ions between the positive and negative electrodes. During charging and discharging, Li+ ions repeatedly insert and extract between the two electrodes: during charging, Li+ ions extract from the positive electrode, pass through the electrolyte, and insert into the negative electrode, leaving the negative electrode in a lithium-rich state; the reverse occurs during discharging.
Lithium-ion batteries were first successfully developed by Sony Corporation of Japan in 1990. They involve embedding lithium ions into carbon (petroleum coke and graphite) to form the negative electrode (traditional lithium batteries use lithium or lithium alloys as the negative electrode). Common positive electrode materials include LixCoO2, LixNiO2, and LixMnO4. The electrolyte is typically LiPF6 + diethylene carbonate (EC) + dimethyl carbonate (DMC).
What are the differences between solid-state batteries and lithium-ion batteries?
The main difference between solid-state batteries and lithium-ion batteries lies in the electrolyte. Lithium-ion batteries use a liquid electrolyte, existing in the form of a gel or polymer, making it difficult to reduce battery weight. Furthermore, a single lithium-ion battery pack has low energy density, necessitating multiple packs connected in series, further increasing weight. The engineering, manufacturing, and installation costs of battery packs account for a significant proportion of the overall cost of an electric vehicle.
Besides weight issues, electrolytes are also flammable, unstable at high temperatures, and prone to thermal runaway, potentially causing serious fires in the event of a car accident. Electrolytes also freeze easily at low temperatures, reducing battery life. Furthermore, electrolytes can corrode internal battery components, and the charging and discharging process can generate dendrites, reducing battery capacity, performance, and lifespan.
Solid-state batteries do not contain a heavy liquid electrolyte; instead, they use a solid electrolyte in the form of glass, ceramic, or other materials. While their overall structure and charging/discharging methods are similar to traditional lithium-ion batteries, the absence of liquid makes them more compact, smaller, and increases energy density. Theoretically, replacing lithium-ion batteries in electric vehicles with solid-state batteries of the same volume could more than double the capacity.
Moreover, solid-state lithium batteries are lighter and do not require the monitoring, cooling, and insulation systems of lithium-ion batteries, freeing up more space in the chassis to house the battery and greatly increasing the range of electric vehicles.
In addition, solid-state batteries charge faster than lithium-ion batteries, do not have corrosion issues, and have a longer lifespan. Regarding operating temperature, solid-state batteries have thermal stability and will not freeze at low temperatures, which ensures the range of electric vehicles for users living in mid- to high-latitude regions.
