The characteristics and price of lithium-ion batteries are closely related to its positive electrode material. Generally speaking, the positive electrode material should meet: (1) Within the required charge and discharge potential range, it has electrochemical compatibility with the electrolyte solution; ( 2) Gentle electrode process kinetics; (3) Highly reversible; (4) Good stability in the air under full lithium state.
Lithium Ion Battery
With the development of lithium-ion batteries, research work on high-performance and low-cost cathode materials is constantly being carried out. At present, research is mainly focused on lithium transition metal oxides such as lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide.
Lithium cobalt oxide (LiCo02) belongs to the a-NaFe02 type structure with a two-dimensional layered structure, which is suitable for the deintercalation of lithium ions. Due to its simple preparation process, stable performance, high specific capacity, and good cycle performance, most of the current commercial lithium-ion batteries use LiCo02 as the cathode material. Its synthesis methods mainly include high-temperature solid-phase synthesis and low-temperature solid-phase synthesis, as well as soft chemical methods such as oxalic acid precipitation method, sol-gel method, cold and heat method, and organic mixing method.
Lithium nickel oxide (LiNi02) is a rock salt structure compound with good high temperature stability. Due to the low self-discharge rate, low requirements for electrolyte, no pollution to the environment, relatively abundant resources and reasonable price, it is a promising cathode material to replace lithium cobalt oxide. At present, LiNi02 is mainly synthesized by solid-phase reaction of Ni(NO3)2, Ni(OH)2, NiCO3, NiOOH and LiOH, LiN03 and LiC03. The synthesis of LiNi02 is more difficult than LiCo02. The main reason is that the stoichiometric LiNi02 is easily decomposed into Li1-xNi1+x02 under high temperature conditions. Excess nickel ions are in the lithium layer between the Ni02 planes, hindering the diffusion of lithium ions. It will affect the electrochemical activity of the material, and because Ni3+ is more difficult to obtain than Co3+, the synthesis must be carried out in an oxygen atmosphere [2]
Lithium manganese oxide is a modification of traditional positive electrode materials. Spinel LixMn204 is currently most widely used, which has a three-dimensional tunnel structure and is more suitable for deintercalation of lithium ions. Lithium manganese oxide has abundant raw materials, low cost, no pollution, overcharge resistance and better thermal safety. It has relatively low requirements for battery safety protection devices, and is considered to be the most promising cathode material for lithium ion batteries. The dissolution of Mn, the Jahn-Telle effect, and the decomposition of the electrolyte are considered to be the main reasons for the capacity loss of lithium-ion batteries with lithium manganese oxide as the cathode material.
