The improvement of power battery performance is inseparable from the progress of battery material technology. At the same time, the improvement of material technology level has greatly promoted the development of power battery technology. The two complement each other and promote each other.
1. Positive electrode material
Cathode materials with high specific capacity, high specific power, high safety and long cycle life have become a hot spot in research and development and industrialization. Generally, the following conditions should be met: (1) Within the required charge-discharge potential range, it has good compatibility with the electrolyte. Compatibility; ② mild electrode process kinetics; ③ good reversibility; ④ good stability in the fully lithiated state.
Its structure should have the following characteristics: ① layered or tunnel structure to facilitate the de-intercalation of lithium ions, and there is no structural change during lithium ion de-insertion, so as to ensure that the electrode has good reversible performance; ② the intercalation and intercalation of lithium ions The amount of extraction is large, the electrode has a higher capacity, and the free energy of the electrode reaction does not change much when the lithium ion is deintercalated, so as to ensure the stable charging and discharging voltage of the battery; ③ The lithium ion should have a larger diffusion coefficient, Generally, a transitional lithium-containing metal compound is selected as the positive electrode material.
At present, the cathode materials that have been produced on a large scale mainly include layered lithium cobalt oxide, nickel-cobalt-manganese ternary materials (including nickel-cobalt-aluminum) and lithium-rich manganese-based materials, spinel-structured lithium manganese oxide and olivine-type structure of lithium iron phosphate, etc.
(1) Lithium cobaltate has good structural stability and high specific capacity. Its tap density and pole piece compaction density are the highest among existing materials, which can meet the requirements of high volume energy density batteries, but it is expensive and cobalt resources are scarce. And poor safety, generally not used in the field of power batteries.
(2) Nickel-cobalt-manganese ternary material has high specific capacity and high tap density. The problems of poor cycle performance and safety can be improved by coating and doping. At present, nickel-cobalt-manganese ternary materials (types 111 and 523, the ratio between nickel, cobalt and manganese elements is 1:1:1 and 5 : 2: 3) has been applied in the field of power batteries on a large scale, ternary materials with higher nickel content (type 622 and 811, the ratio between nickel, cobalt and manganese elements is 6: 2: 2 and 8: 1: 1 ) is currently in the process of development and application verification in the field of power batteries.
(3) The specific capacity of the nickel-cobalt-aluminum ternary material is high, which is close to that of the lithium cobalt oxide material. It is necessary to further improve the safety, reduce the residual alkali content and gas production. The precursor of the nickel-cobalt-aluminum ternary material has formed a stable production capacity. The aluminum ternary material has been developed and is in the process of application and promotion in the field of power batteries.
(4) Lithium manganese oxide has three-dimensional lithium ion diffusion channels, low raw material cost, simple production process, good thermal stability, good overcharge resistance, high discharge voltage platform, and good safety, but the high temperature cycle performance and storage performance are poor. , which can be improved by coating aluminum oxide on the surface and applied to power batteries.
(5) Lithium iron phosphate has good safety and long cycle life. It can improve the problems of low tap density and poor low temperature rate performance through nanometerization, coating and doping. It has been applied to power batteries on a large scale.
(6) High-voltage, high-capacity lithium-rich manganese-based materials and high-voltage spinel lithium manganese oxide materials are still in the process of development and verification. At present, the products of foreign power battery companies are mainly lithium manganese oxide, nickel cobalt manganese, nickel cobalt aluminum or their mixed materials.
Lithium iron phosphate materials account for a large proportion of the products of Chinese power battery companies. With the substantial increase in the specific energy requirements of power batteries (>300W·h/kg) by automobile companies, the trend and speed of Chinese power battery companies are accelerating towards nickel-cobalt-manganese, nickel-cobalt-aluminum or their mixture with lithium manganese oxide materials.
The development status of cathode material technology for power battery is shown in the following table.
2. Negative electrode material
Anode materials with high specific capacity, high charge-discharge efficiency, high cycle performance and low cost have become a hot spot in research, development and industrialization. Generally, the following conditions should be met: ① good electronic conductivity; ② large lithium ion diffusion coefficient; ③ Small volume change before and after lithium intercalation; (4) high reversible capacity of lithium intercalation; (5) small change in reaction free energy and low lithium intercalation potential; (6) high reversibility;
At present, the large-scale production of anode materials mainly includes layered carbon materials (including artificial graphite, natural graphite, mesocarbon microspheres, soft carbon and hard carbon, etc.), alloy materials (including silicon-based and tin-based materials) etc.) and oxide materials (such as lithium titanate materials, etc.).
Among them, artificial graphite, natural graphite and mesophase carbon microspheres have mature technologies and supporting processes, but the specific capacity has reached the limit and the safety is poor. They have been widely used in the field of power batteries. Soft carbon has fast charge and discharge, good low temperature performance and cycle performance and cost advantages, but the first time efficiency is low, and it is mainly used in the field of power batteries mixed with graphite materials. Hard carbon has good rate performance and safety performance, but it has low efficiency and high cost for the first time. It is mainly used in the field of power batteries mixed with graphite materials.
Silicon-based alloy materials have the characteristics of abundant raw materials and high capacity, but the initial efficiency is low, the volume changes during the cycle process, and it is easy to pulverize. It is currently in the process of development and application verification in the field of power batteries. Lithium titanate material has excellent rate performance, high and low temperature performance, cycle performance and safety, but high cost and low energy density. In recent years, the flatulence problem has been basically solved by surface modification and electrolyte matching, and it has been used in the field of power batteries.
At present, graphite materials are the mainstream choices of power battery companies at home and abroad (including artificial graphite, natural graphite and mesocarbon microspheres, etc.). With the significant increase in the specific energy requirements of power batteries (>300W·h/kg) by automobile companies, alloy materials, especially silicon-based composite materials, have become the focus of current application research and industrialization.
At present, related products have been launched ( Reversible specific capacity>450mA·h/g, mainly used in consumer lithium-ion batteries), in plug-in hybrid vehicles with both energy and power and fast charging power batteries, the hybrid material of graphite and soft carbon is realized. And the batch application of lithium titanate materials.
The development status of anode material technology for power battery is shown in the following table.
China has entered the forefront of the world in the research and development and industrialization of anode materials, which can meet the needs of power battery enterprises for anode materials.