Nickel-cobalt-manganese has the characteristics of high specific capacity, long cycle life, low toxicity and low cost. In addition, there is 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 content of nickel in the material is one of the current research hotspots.
1 high nickel ternary material
Generally speaking, high-nickel ternary cathode materials refer to the mole fraction of nickel in the material is greater than 0.6. Such ternary materials have the characteristics of high specific capacity and low cost, but also have low capacity retention and poor thermal stability. defect.
The performance of the material can be effectively improved by improving the preparation process. The micro-nano size and morphology of the particles largely determine the performance of high-nickel ternary cathode materials. Therefore, the current important preparation method is to uniformly disperse different raw materials and obtain nano-spherical particles with large specific surface area through different growth mechanisms.see more:accidentally left battery in checked luggage
Among the 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 raw material mixing and uniform particle size, and then high-temperature calcination to obtain a regular surface morphology. The ternary material whose process is easy to control is an important method for industrial production at present.
The spray-drying method is simpler than the coprecipitation method, and the preparation speed is faster. The morphology of the obtained material is not inferior to the coprecipitation method, and 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 the conductivity, cycle performance, rate performance, storage performance, and high-temperature and high-pressure performance will still be a research hotspot.
2 Lithium-rich ternary materials
All of this material has the characteristics of high voltage, and the first charging and discharging mechanism is different from the subsequent charging: the first charging will cause structural changes, and this change is reflected in the charging curve. There are two different platforms with 4.4V as the boundary, In the second charging process, the charging curve is different from the first charging curve, because Li2O is irreversibly released from the layered Li2MnO3 in the first charging process, and the plateau at about 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. Among them, the co-precipitation method is more commonly used, and each Each method has its own advantages and disadvantages.
Lithium-rich ternary materials have shown good application prospects and are one of the key materials required for the next generation of high-capacity lithium-ion batteries, but for large-scale applications.
The future research direction of this material is mainly the following aspects:
(1) Insufficient understanding of the mechanism of lithium deintercalation, unable to explain the phenomenon of low Coulombic efficiency of materials and large differences in material properties;
(2) The research on doping elements is not sufficient and relatively single;
(3) Due to the corrosion of the positive electrode material by the electrolyte under high voltage, poor cycle stability is caused;
(4) There are few commercial applications, and the investigation of safety performance is not comprehensive enough. 3 Single crystal ternary cathode material
Lithium battery ternary materials under high voltage, as the number of cycles increases, secondary particles or agglomerated single crystals may appear in the later stage of pulverization of the primary particle interface or separation of agglomerated single crystals, resulting in increased internal resistance and battery failure. The capacity fades quickly and the cycle becomes worse.
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. First, 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 is still 98% of the initial discharge capacity after 1300 cycles. , is a ternary cathode composite material with excellent electrochemical performance.
The positive electrode material production line is the first large-scale production of micron-sized single crystal particle modified spinel lithium manganese oxide and nickel-cobalt lithium manganate ternary positive electrode materials in the world, reaching an annual production capacity of 500 tons.
4 graphene doping
Graphene has a two-dimensional structure of single-layer atomic thickness, stable structure, and electrical conductivity up to 1×106S/m. The use of graphene in lithium-ion batteries has the following advantages: ①Good electrical and thermal conductivity, which helps to improve the rate performance and safety of the battery; ②Compared to graphite, graphene has more space for lithium storage, which can increase the energy density of the battery; ③The particle size is on the micro-nano scale, and the diffusion path of lithium ions is short, which is conducive to improving 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 window. However, due to the low electrochemical stability window of the current commercial carbonate-based electrolytes, high-voltage cathode materials have not been industrialized so far.
When the battery voltage reaches about 4.5 (vs. Li/Li+), the electrolyte begins to oxidize and decompose violently, resulting in the failure of the lithium intercalation and removal reactions 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, nonflammability, 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 effectively improve the oxidation stability of the electrolyte. And most of the new organic solvents have the advantages of low flammability, which is 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 leads to the cycle stability of battery negative electrode materials and battery life. Magnification performance is degraded.
In high-voltage electrolytes, film-forming additives are also essential components, common ones include tetraphenylphosphineamide, LiBOB, lithium difluorodioxalate borate, tetramethoxytitanium, succinic anhydride, and trimethoxyphosphine Wait.
A small amount (<5%) of film-forming additives are added to the carbonate-based electrolyte to make oxidation/reduction decomposition reactions occur preferentially over solvent molecules, and to form an effective protective film on the electrode surface, which can inhibit carbonate-based solvents subsequent decomposition. The film formed by the additive with excellent performance can even inhibit the dissolution of metal ions in 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 the co-precipitation method, and the surfactant, ultrasonic vibration and mechanical stirring are used together. Finally, the prepared flake 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 used.
It is found that using OA and PVP as surfactants can prepare regular hexagonal nanosheet-shaped cathode material precursors with excellent morphology, and the particle size distribution of the obtained nanosheets is relatively uniform, with a size of about 400nm. Surfactants have a great influence on the precursor. Good shape control application, the first discharge specific capacity of the assembled battery at 1C discharge rate is 157.093mAh˙g-1, and the capacity retention rate after 50 cycles at 1C, 2C, 5C and 10C discharge rate is greater than 92 %, showing good electrochemical performance.
7 microwave synthesis method
Among the important methods for preparing ternary cathode materials, the 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 the bulk heating caused by the dielectric loss of materials in the electromagnetic field. The heating speed is fast and uniform, and the synthesized materials often have better structures and properties. It is a very potential way to synthesize cathode materials.
The structure, micro-morphology and electrochemical performance of the synthesized materials were characterized by means of XRD, SEM and charge-discharge. The experimental results show that the positive electrode material synthesized in the microwave with an output power of 1300W, under the charge and discharge condition of 0.2C, the first discharge specific capacity is as high as 185.2mAh/g, the Coulombic 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 method
When infrared rays irradiate a 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, and vibration and rotation Raise 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 adopts a new infrared heating and roasting technology to prepare ternary materials. First, nickel-cobalt-manganese-lithium acetate is mixed evenly 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 a nitrogen atmosphere at ℃ for 3 hours. In the voltage range of 2.8-4.5V, the capacity retention rate was as high as 94% after 50 cycles of 1C discharge, and the specific capacity of the first cycle reached 170mAh/ g, 5C is 75mAh/g, and the high rate performance needs to be improved.
When the traditional high-temperature calcination method is used to prepare ternary cathode materials, the synthesis temperature is high, the calcination time is long, and the energy loss is large.Also read:Marine Lithium Battery
The study found that in a 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. Mix the oxide of nickel-cobalt-manganese and lithium carbonate evenly, then put it into a plasma generator, and react at 600°C for 20-60 minutes under the condition of feeding oxygen to obtain the ternary positive electrode material Li(Ni1/3Co1/3Mn1 /3) O2.
The prepared cathode material has a high initial discharge specific capacity of 218.9mAh˙g-1, and the cycle stability, rate 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 positive electrode materials of lithium-ion batteries accounts for 30%-40%. Therefore, the energy storage performance of positive electrode materials can be recovered by using the preparation process by recycling waste battery positive electrode materials, 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 has invested 100 million yuan to build the largest waste battery and scrap battery material processing production line in China. The annual recovery and utilization of cobalt resources is more than 4,000 tons, accounting for more than 30% of my country's strategic cobalt resource supply. Come, the recycling featured route to a new battery.
The whole production line is made of recycled nickel, cobalt, and manganese from waste batteries, and the 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 production in October 2014, it has achieved an output value of nearly 200 million yuan, and it is expected to achieve an output value of 500 to 600 million yuan in the future.