I. Materials
In terms of materials used, polymer lithium-ion batteries can be categorized into four types: cathode materials (lithium cobalt oxide, lithium manganese oxide, ternary materials, and lithium iron phosphate), and anode materials (graphite). The working principles are also largely the same. The key difference between the cathode materials of polymer lithium-ion batteries lies in the electrolyte. Liquid lithium-ion batteries use liquid electrolytes, while polymer lithium-ion batteries use solid polymer electrolytes. This polymer can be dry or gel-like; currently, most use polymer gel electrolytes.
Ternary lithium batteries use lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide as the cathode material. Ternary composite cathode materials are made from nickel salts, cobalt salts, and manganese salts. The ratio of nickel, cobalt, and manganese can be adjusted according to actual needs. Batteries with ternary materials as cathodes are safer than lithium cobalt oxide batteries, but the voltage is too low.
Lithium iron phosphate (LFP) batteries, when used as cathode materials, have long charge-discharge cycle life, but their disadvantages include significant gaps in energy density, high and low temperature performance, and charge-discharge rate characteristics, as well as high production costs. LFP battery technology and applications have encountered development bottlenecks. Lithium manganese oxide (LMO) batteries have low energy density, poor cycle stability at high temperatures, and poor storage performance, thus LMO was only used as the cathode material for the first generation of international power lithium batteries. Meanwhile, multi-element materials, due to their combined advantages in performance and cost, are increasingly attracting industry attention and recognition, gradually surpassing LFP and LMO to become the mainstream technology route.
II. Performance
Polymer lithium batteries offer the following performance characteristics: more flexible design, higher specific energy, wider electrochemical stability window, higher safety and reliability, longer cycle life, slower capacity decay, higher volume utilization, lower internal resistance, lighter weight, and lower self-discharge.
The performance characteristics of ternary lithium batteries are as follows: In terms of safety, they are safer than lithium cobalt oxide batteries, but lower than lithium iron phosphate batteries. Among all commercially available lithium-ion batteries, their safety level is moderate and still needs improvement. In terms of energy density, they far exceed lithium cobalt oxide batteries, lithium manganese oxide batteries, and lithium iron phosphate batteries. In terms of voltage, their single cells have an absolute advantage at 3.7V, while lithium iron phosphate is 3.2V and lithium titanate is 2.3V.
Disadvantages of polymer lithium batteries: higher production costs, difficulty in purifying the electrolyte system, need for protection circuit control to prevent overcharging and discharging, damage to the reversibility of internal chemical substances, and serious impact on lifespan.
Disadvantages of ternary lithium batteries: poor high-temperature resistance, limited cycle life, poor high-power discharge performance, toxic elements, and the temperature rises very easily after high-power charging and discharging, releasing oxygen at high temperatures and making them flammable.
