Structural characteristics of lithium-ion batteries
The active materials of both the positive and negative electrodes in a lithium-ion battery are intercalation compounds. During charging, lithium ions are deposited from the positive electrode and inserted into the negative electrode through the electrolyte. In essence, a lithium-ion battery charges and discharges by repeatedly inserting and releasing ions between the two electrodes, hence the name rocking chair battery (RCB). The reaction diagram and basic equations are as follows:
2. Polymer lithium-ion battery technology
2.1 Performance characteristics of polymer lithium-ion batteries
Polymer lithium-ion batteries are lithium-ion batteries that use solid polymer electrolytes (SPEs). The battery consists of a positive electrode collecting liquid, a positive electrode membrane, a polymer electrolyte membrane, a negative electrode membrane, and a negative electrode collecting liquid, all compacted and composite-molded together and sealed with an aluminum-plastic composite membrane, with the edges heat-fused for sealing. Because the electrolyte membrane is solid, there is no leakage problem, and the battery design offers great freedom, allowing for the use of series-parallel or bipolar structures as needed.
Polymer lithium-ion batteries have the following characteristics: flexible shape; higher specific energy (3 times that of MH-Ni batteries); (3) wide electrochemical stability window, up to 5V; (4) perfect safety and reliability; (5) long cycle life and low capacity loss; high capacity utilization rate; and wide range of applications.
Its performance indicators are as follows: operating voltage: 3.8V; specific energy: 130Wh/kg, 246Wh/L; cycle life: >300; self-discharge: <0.1%/month; operating temperature: 253-328K; charging speed: 80% capacity per hour; 100% capacity in 3 hours; environmental factors: non-toxic.
2.2 Cathode Material
The characteristics and price of lithium-ion batteries are closely related to their cathode materials. Generally speaking, cathode materials should meet the following requirements: electrochemical compatibility with electrolyte solution within the required charge and discharge potential range; mild electrode process kinetics; high reversibility; and good air stability under full lithium conditions. With the development of lithium-ion batteries, research on high-performance and low-cost cathode materials is also ongoing. Currently, research mainly focuses on lithium transition metal oxides such as lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide [1] (see Table 1).
