Nickel-Cobalt-Manganese has the characteristics of high specific capacity, long cycle life, low toxicity, and low cost. In addition, it has a good synergistic effect among the three elements, so it has been widely used. Nickel is an important component in redox energy storage for lithium-ion battery cathode materials. How to effectively increase the specific capacity of the material by increasing the nickel content in the material is one of the current research hotspots.
1 High nickel ternary material
Generally speaking, high-nickel ternary cathode material means that the mole fraction of nickel in the material is greater than 0.6. Such a ternary material has the characteristics of high specific capacity and low cost, but also has low capacity retention rate, poor thermal stability, etc. defect.
The material properties can be effectively improved through the improvement of the preparation process. The micro-nano size and morphological structure of the particles determine the performance of the high-nickel ternary cathode material to a large extent. Therefore, an important preparation method at present is to uniformly disperse different raw materials and obtain nano-spherical particles with large specific surface area through different growth mechanisms.Also read:48v lithium ion battery 200ah
Among many preparation methods, the combination of co-precipitation method and high-temperature solid-phase method is the current mainstream method. First, the co-precipitation method is used to obtain a precursor with uniform mixing of raw materials and uniform particle size of the material. The ternary material whose process is easy to control is an important method for industrial production at present.
Compared with the co-precipitation method, the spray-drying method has a simpler process and a faster preparation speed, and the morphology of the obtained material is no less than that of the co-precipitation method, which has the potential for further research. The shortcomings of high nickel ternary cathode materials such as cation mixing and phase transition during charge and discharge can be effectively improved by doping modification and coating modification. While suppressing the occurrence of side reactions and stabilizing the structure, improving electrical conductivity, cycling performance, rate performance, storage performance, and high temperature and high pressure performance will remain a research hotspot.
2 Lithium-rich ternary materials
All of this material has the characteristics of high voltage, and the first charge and discharge mechanism is different from the subsequent charge: the first charge will cause a change in structure, which is reflected in the charge curve with two different plateaus demarcated by 4.4V, During the second charging process, the charging curve is different from that of the first charging process. Due to the irreversible release of Li2O from the layered Li2MnO3 during the first charging process, the plateau at around 4.5V disappears.
Lithium-rich ternary cathode materials with different structures can be prepared by solid-phase method, sol-gel method, hydrothermal method, spray pyrolysis method and co-precipitation method. Each method has its own advantages and disadvantages.
Lithium-rich ternary materials show good application prospects and are one of the key materials required for the next generation of high-capacity lithium-ion batteries, but they are not about large-scale applications.
The future research directions of this material are mainly in the following aspects:
(1) The understanding of the mechanism of lithium deintercalation is insufficient, and it is impossible to explain the phenomenon that the coulombic efficiency of the material will be low and the material performance will vary greatly;
(2) The research on doping elements is not sufficient and relatively single;
(3) Poor cycle stability due to the corrosion of the positive electrode material by the electrolyte at high voltage;
(4) There are few commercial applications, and the investigation on safety performance is not comprehensive enough. 3Single crystal ternary cathode material
At high voltage, as the number of cycles increases, the secondary particles or agglomerated single crystals may be pulverized at the interface of the primary particles or the agglomerated single crystals may be separated in the later stage, resulting in increased internal resistance and battery. The capacity decays quickly and the cycle becomes worse.Also read:48v lithium ion battery 400ah
The single-crystal high-voltage ternary material can improve the lithium ion transfer efficiency and reduce the side reaction between the material and the electrolyte, thereby improving the cycle performance of the material under high voltage. Firstly, the ternary material precursor is prepared by co-precipitation method, and then single crystal LiNi0.5Co0.2Mn0.3O2 is obtained under the application of high temperature solid phase.
This material has a good layered structure. At 3-4.4V, the 0.1 discharge specific capacity of the button battery can reach 186.7mAh/g, and the discharge specific capacity of the full battery after 1300 cycles is still 98% of the initial discharge capacity. , is a ternary cathode composite material with excellent electrochemical performance.
The cathode material production line is the first international large-scale production of micron-sized single crystal particle modified spinel lithium manganate and nickel-cobalt lithium manganate ternary cathode materials, with an annual production capacity of 500 tons.
4 Graphene doping
Graphene has a two-dimensional structure with a single-layer atomic thickness, which is stable in structure and has an electrical conductivity of up to 1×106S/m. Graphene used in lithium-ion batteries has the following advantages: ① good electrical and thermal conductivity, which helps to improve the rate performance and safety of the battery; ② related to graphite, graphene has a lot of lithium storage space, which can improve the energy density of the battery; ③ The particle size is in the micro-nano scale, and the diffusion path of lithium ions is short, which is beneficial to improve the power performance of the battery.
5 High Voltage Electrolyte
Ternary materials have received more and more attention and research due to their high voltage windows. However, due to the low electrochemical stability window of the current commercial carbonate-based electrolytes, high-voltage cathode materials have not yet been industrialized.
When the battery voltage reaches about 4.5 (vs. Li/Li+), the electrolyte begins to undergo violent oxidative decomposition, resulting in the failure of the lithium intercalation and delithiation reaction of the battery to proceed normally. Improving the stability of the electrode/electrolyte interface by developing and applying new high-voltage electrolyte systems or high-voltage film-forming additives is an effective way to develop high-voltage electrolytes. In energy storage systems, ionic liquids, dinitrile organic compounds and sulfone organic solvents are currently used as electrolytes for high-voltage ternary materials. Ionic liquids with low melting point, non-flammability, low vapor pressure, and high ionic conductivity exhibit excellent electrochemical stability and have been extensively studied.
Replacing all or part of the commonly used carbonate solvents with new solvents with high pressure stability can indeed effectively improve the oxidative stability of electrolytes. And most of the new organic solvents have the advantages of low flammability and are expected to fundamentally improve the safety performance of lithium-ion batteries, but most of the new solvents have poor reduction stability and high viscosity, which lead to the cycle stability of battery anode materials and the battery’s performance. Reduced rate performance.Also read:eve 280ah cells
In high-voltage electrolytes, film-forming additives are also essential components, such as tetraphenylphosphine amide, LiBOB, lithium difluorobisoxalate borate, tetramethoxytitanium, succinic anhydride, and trimethoxyphosphorus Wait.
Add a small amount (<5%) of film-forming additives to the carbonate-based electrolyte, so that the oxidation/reduction decomposition reaction occurs preferentially to the solvent molecules, and an effective protective film is formed on the electrode surface, which can inhibit the carbonate-based solvent subsequent decomposition. The film formed by the additive with excellent performance can even inhibit the dissolution of the metal ions of the positive electrode material and the deposition on the negative electrode, thereby significantly improving the stability of the electrode/electrolyte interface and the cycle performance of the battery.
6 Surfactant-assisted synthesis
The performance of the ternary cathode material depends on the preparation method. It is prepared by co-precipitation method, and synergistically used by surfactant, ultrasonic vibration and mechanical stirring. Finally, the prepared sheet precursor and lithium carbonate are annealed at high temperature to grow into a ternary layer. The structure is a new type of ternary cathode material synthesis process currently adopted.
It is found that the use of OA and PVP as surfactants can prepare regular hexagonal nanosheet-like cathode material precursors with excellent morphology, and the particle size distribution of the obtained nanosheets is relatively uniform, with a size of about 400 nm, and the surfactants have a good effect on the precursors. Good shape control application, the first discharge specific capacity of the assembled battery at the discharge rate of 1C is 157.093mAh˙g-1, and the capacity retention rate is greater than 92 after 50 cycles at the discharge rate of 1C, 2C, 5C and 10C. %, showing good electrochemical performance.
7 Microwave synthesis method
Among the important methods for preparing ternary cathode materials, solid-phase method, co-precipitation method and sol-gel method all need to be sintered at high temperature for several hours, which consumes a lot of energy and the preparation process is complicated. Microwave heating is bulk heating caused by dielectric loss of materials in an electromagnetic field. The heating speed is fast and uniform, and the synthesized materials often have better structure and performance. It is a very potential way to synthesize cathode materials.
The structure, microstructure and electrochemical properties of the synthesized materials were characterized by means of XRD, SEM and charge-discharge. The experimental results show that the cathode material synthesized in the microwave with the output power of 1300W, under the condition of 0.2C charge and discharge, the first discharge specific capacity is as high as 185.2mAh/g, the Coulomb efficiency is 84%, and the capacity is maintained at 92.3% after 30 cycles. (2.8-4.3V), showing good electrochemical performance and application potential. 8 Infrared synthesis methods
When infrared rays irradiate the heated object, when the emitted infrared wavelength is consistent with the absorption wavelength of the heated object, the heated object absorbs infrared rays, and the molecules and atoms inside the object resonate, resulting in strong vibration and rotation, while vibration and rotation Increase the temperature of the object to achieve the purpose of heating.
Using this heating principle, it can be used to prepare ternary cathode materials. HSIEH uses a new infrared heating roasting technology to prepare ternary materials. First, the nickel cobalt manganese lithium acetate is mixed with water, and then a certain concentration of glucose solution is added. The carbon-coated 333-type ternary cathode material was prepared in one step under nitrogen atmosphere at ℃ for 3 hours. In the voltage range of 2.8-4.5V, 50 cycles of 1C discharge, the capacity retention rate was as high as 94%, and the specific capacity of the first cycle of discharge reached 170mAh/ g, 5C is 75mAh/g, and the high rate performance needs to be improved.
When the ternary cathode material is prepared by the traditional high temperature calcination method, the synthesis temperature is high, the calcination time is long, and the energy loss is large.
The study found that in the low temperature plasma environment, the chemical activity of each reactant is high and the chemical reaction speed is fast, which can realize the rapid preparation of ternary cathode materials. The oxides of nickel cobalt manganese and lithium carbonate are mixed uniformly, and then placed in a plasma generator, under the condition of introducing oxygen, and reacting at 600 ° C for 20 to 60 minutes to obtain a ternary cathode material Li (Ni1/3Co1/3Mn1 /3) O2.
The prepared cathode material has a high initial discharge specific capacity of 218.9 mAh˙g-1, while the cycle stability, rate capability and high temperature performance are also due to the materials prepared by traditional methods.
10 Preparation of ternary cathode materials from waste batteries
The cost of cathode materials for lithium-ion batteries accounts for 30%-40%. Therefore, the energy storage performance of cathode materials can be recovered by recycling the cathode materials of waste batteries and the preparation process, which can greatly reduce the cost of lithium-ion batteries, and a complete The lithium-ion battery industry chain should include the recycling of lithium-ion batteries.
GEM invested 100 million yuan to build the largest production line for waste batteries and waste battery materials in my country, recycling more than 4,000 tons of cobalt resources annually, accounting for more than 30% of my country’s strategic cobalt resource supply, forming GEM’s battery materials from waste batteries. Come on, the recycling feature route to new batteries.
The entire production line is made of nickel, cobalt, and manganese recycled from waste batteries into a solution, and a synthetic agent is added. After a series of processes, it becomes the positive electrode material of nickel-cobalt-manganese ternary power lithium-ion battery. Since it was put into operation in October 2014, it has achieved an output value of nearly 200 million yuan, and is expected to achieve an output value of 500 to 600 million yuan in the future.