Nickel Metal Hydride No. 5 battery.Research and latest progress of nickel-cobalt-manganese ternary materials in lithium batteries

Electronic enthusiasts provide you with the research and latest progress of nickel-cobalt-manganese ternary materials in lithium batteries. Nickel-cobalt-manganese ternary materials are a new type of lithium-ion battery cathode materials developed in recent years. They have high capacity and good cycle stability. , moderate cost and other important advantages. Because this type of material can effectively overcome the problems of high cost of lithium cobalt oxide materials, low stability of lithium manganate materials, and low capacity of lithium iron phosphate, it has been successfully used in batteries. And the application scale has developed rapidly.

Nickel-cobalt-manganese ternary materials are a new type of lithium-ion battery cathode materials developed in recent years. They have important advantages such as high capacity, good cycle stability, and moderate cost. This type of material can effectively overcome the high cost of lithium cobalt oxide materials at the same time. Problems such as low stability of lithium manganate materials and low capacity of lithium iron phosphate have been successfully applied in batteries, and the scale of application has developed rapidly.

According to disclosures, the output value of China's lithium-ion battery cathode materials reached 9.575 billion yuan in 2014, of which ternary materials accounted for 2.74 billion yuan, accounting for 28.6%. In the field of power batteries, ternary materials are rising strongly. The BAIC EV200 launched in 2014 , Chery eQ, JAC iEV4, Zotye Cloud 100, etc. all use ternary power batteries.

At the 2015 Shanghai International Auto Show, among new energy vehicles, the share of ternary lithium batteries exceeded that of lithium iron phosphate batteries and became a highlight. Most mainstream domestic car companies including Geely, Chery, Changan, Zotye, and China have launched New energy models using ternary power batteries. Many experts predict that ternary materials are expected to replace expensive lithium cobalt oxide materials in the near future with their excellent performance and reasonable manufacturing costs.

It was found that the proportion of nickel, cobalt and manganese in the nickel-cobalt-manganese ternary cathode material can be adjusted within a certain range, and its performance changes with the different proportions of nickel-cobalt-manganese. Therefore, in order to further reduce high-cost transition metals such as cobalt and nickel, content, and the purpose of further improving the performance of cathode materials; countries around the world have done a lot of work in the research and development of ternary materials with different nickel-cobalt-manganese compositions, and have proposed a number of ternary materials with different nickel-cobalt-manganese ratios. Ternary material system. Including 333, 523, 811 system, etc. Some systems have successfully achieved industrial production and application.

This article will systematically introduce the latest research progress and results of several major nickel-cobalt-manganese ternary materials in recent years, as well as some research progress in doping, coating, etc. carried out in order to improve the properties of these materials.
1 Structural characteristics of nickel-cobalt-manganese ternary cathode material

Nickel-cobalt-manganese ternary materials can usually be expressed as: LiNixCoyMnzO2, where x+y+z=1; depending on the molar ratio of the three elements (x:y:z ratio), they are called different systems, such as A ternary material with a nickel-cobalt-manganese molar ratio (x:y:z) of 1:1:1 is referred to as type 333. A system with a molar ratio of 5:2:3 is called the 523 system, etc.

Ternary materials such as type 333, type 523 and type 811 all belong to the α-NaFeO2 type layered rock salt structure of the hexagonal crystal system, as shown in Figure 1.

In the nickel-cobalt-manganese ternary material, the main valence states of the three elements are +2, +3 and +4, with Ni being the main active element. The reaction and charge transfer during charging are shown in Figure 2.

Generally speaking, the higher the content of active metal components, the greater the capacity of the material. However, when the content of nickel is too high, it will cause Ni2+ to occupy the Li+ position, exacerbating the cation mixing, resulting in a reduction in capacity. Co can suppress cation mixing and stabilize the layered structure of the material; Mn4+ does not participate in electrochemical reactions, providing safety and stability while reducing costs.
2 Latest research progress in preparation technology of nickel-cobalt-manganese ternary cathode materials

Solid phase method and co-precipitation method are the main methods of traditional preparation of ternary materials. In order to further improve the electrochemical properties of ternary materials, while improving solid phase method and co-precipitation method, new methods such as sol-gel, spray drying, Spray pyrolysis, rheological phase, combustion, thermal polymerization, template, electrospinning, molten salt, ion exchange, microwave assistance, infrared assistance, ultrasonic assistance, etc. are proposed.

2.1 Solid phase method

OHZUKU, the founder of ternary materials, initially used the solid-phase method to synthesize 333 materials. The traditional solid-phase method only uses mechanical mixing, so it is difficult to prepare ternary materials with uniform particle size and stable electrochemical properties. To this end, HE, LIU, etc. use low melting point nickel cobalt manganese acetate and roast it at a temperature higher than the melting point. The metal acetate becomes a fluid state and the raw materials can be mixed well. A certain amount of oxalic acid is mixed into the raw materials to alleviate agglomeration and is prepared. The scanning electron microscopy (SEM) of the 333 produced shows that its particle size is uniformly distributed around 0.2-0.5 μm, and the first-cycle discharge specific capacity at 0.1C (3-4.3V) can reach 161mAh/g. TAN et al. use nanorods as the manganese source to prepare 333 particles with a particle size uniformly distributed between 150 and 200nm.

The primary particle size of materials produced by the solid-phase method ranges from 100 to 500 nm. However, due to high-temperature roasting, primary nanoparticles can easily agglomerate into secondary particles of different sizes. Therefore, the method itself needs further improvement.

2.2 Co-precipitation method

The co-precipitation method is a method based on the solid-phase method. It can solve the problems of uneven mixing and excessive particle size distribution in the traditional solid-phase method. By controlling the concentration of raw materials, dropping speed, stirring speed, pH value and reaction temperature, Preparation of ternary materials with various shapes such as core-shell structure, sphere, nanoflower, etc. and relatively uniform particle size distribution.

Raw material concentration, dripping speed, stirring speed, pH value and reaction temperature are key factors in preparing ternary materials with high tap density and uniform particle size distribution. LIANG et al. controlled pH=11.2, complexing agent ammonia concentration 0.6mol/L, and stirred At a speed of 800r/min, T=50℃, a 622 material with a tap density of 2.59g/cm3 and uniform particle size distribution was prepared (Figure 3). After 100 cycles of 0.1C (2.8~4.3V), the capacity retention rate was as high as 94.7 %.

In view of the high specific capacity of 811 ternary material (up to 200mAh/g, 2.8~4.3V), 424 ternary material can provide excellent structure and thermal stability characteristics. Some researchers tried to synthesize a ternary material with a core-shell structure (the core is 811 and the shell l is 424). HOU and others used distributed precipitation and first pumped 8:1:1 (nickel After the 811 core is formed, pump in the raw material solution with a nickel, cobalt and manganese ratio of 1:1:1 to form the first shell layer, and then pump in the original solution with a composition of 4:2:2 , and finally prepared a 523 material with a core composition of 811 and a double-layer shell with shell compositions of 333 and 424 with excellent cycle performance. At 4C rate, the capacity retention rate of this material after 300 cycles reaches 90.9%, while that of 523 prepared by the traditional precipitation method is only 72.4%.

HUA et al. used a co-precipitation method to prepare linear gradient 811 type. From the core of the particle to the surface, the nickel content decreases and the manganese content increases. From Table 1, it can be clearly seen that the discharge capacity of the 811 ternary material with linear gradient distribution at high rates is And the cyclicity is significantly better than the 811 type with evenly distributed elements.

Nano-ternary materials, with their large surface area, short Li+ migration path, high ion and electronic conductivity, and excellent mechanical strength, can greatly improve battery performance at high rates.

HUA et al. used a rapid co-precipitation method to prepare nanoflower-shaped type 333. The 3D nanoflower-shaped type 333 not only shortens the Li+ migration path, but its special surface morphology provides enough channels for Li+ and electrons, which also It well explains why this material has excellent rate performance (2.7~4.3V, under 20C fast charge, the discharge specific capacity reaches 126mAh/g).

Due to the excellent complexing properties of ammonia and metal ions, ammonia is commonly used as the complexing agent in the co-precipitation method. However, ammonia is corrosive and irritating, and is harmful to both humans and aquatic animals, even at very low concentrations (>300mg/ L), so KONG et al. tried to use the low-toxicity complexing agent oxalic acid and the green complexing agent sodium lactate to replace ammonia water. The 523 material prepared with sodium lactate as the complexing agent has better 0.1C and 0.2C performance than ammonia water as the complexing agent. Type 523 prepared from the agent.

2.3 Sol-gel method

The biggest advantage of the sol-gel method is that it can achieve uniform mixing of reactants at the molecular level in a very short time. The prepared materials have uniform distribution of chemical components, precise stoichiometric ratios, small particle sizes and well-distributed materials. Narrow and other advantages.

MEI et al. used an improved sol-gel method: citric acid and ethylene glycol were added to a certain concentration of lithium nickel cobalt manganese nitrate solution to form a sol, and then an appropriate amount of polyethylene glycol (pEG-600) was added. pEG not only serves as a dispersion Agent, and also used as a carbon source, the 333 ternary material with a particle size distribution of about 100 nm and a carbon-coated core-shell structure was synthesized in one step. The capacity retention rate after 100 cycles of 1C cycle reached 97.8% (2.8~4.6V, first cycle discharge Capacity 175mAh/g). YANG et al. investigated the impact of different preparation methods (sol-gel, solid phase method and precipitation method) on the performance of type 424. The charge and discharge test results showed that the 424 material prepared by the sol-gel method has a higher discharge capacity.

2.4 Template method

Relying on its spatial confinement and structure guidance, the template method is widely used in the preparation of materials with special morphology and precise particle size.

WANG et al. used carbon fibers (VGCFs) as templates (Figure 4), used COOH on the surface of VGCFs to adsorb metal nickel, cobalt and manganese ions, and roasted them at high temperature to produce nanoporous 333 ternary materials.

On the one hand, the nanoporous 333-type particles can greatly shorten the lithium ion diffusion path. On the other hand, the electrolyte can infiltrate into the nanopores to add another channel for Li+ diffusion. At the same time, the nanopores can also buffer the volume changes of long-cycle materials, thereby improving Material stability. These advantages enable Type 333 to achieve excellent rate and cycle performance on aqueous lithium-ion batteries: 45C charge and discharge, first cycle discharge specific capacity of 108mAh/g, 180C charge, 3C discharge, 50 cycles, and a capacity retention rate of 95%. .

XIONG et al. used porous MnO2 as a template agent and LiOH as a precipitant, precipitating nickel and cobalt on the MnO2 pores and surface, and then prepared 333 type through high-temperature roasting. Compared with the traditional precipitation method, the 333 ternary material prepared by the template method has Better rate performance and stability.

2.5 Spray drying

The spray drying method is regarded as a method of producing ternary materials with very broad application prospects due to its advantages such as high degree of automation, short preparation cycle, fine particles with narrow particle size distribution, and no production of industrial wastewater.

OLJACA et al. used a spray drying method to prepare a ternary material composed of 333. At a high temperature of 60 to 150°C, nickel cobalt manganese lithium nitrate was rapidly atomized, the water evaporated in a short time, and the raw materials were quickly mixed, and the final powder was obtained The final 333 ternary material is obtained after roasting at 900°C for 4 hours.

OLJACA et al. believe that by controlling the temperature and residence time during the pyrolysis of raw materials, high-temperature roasting can be greatly shortened or even completely avoided, thereby achieving continuous, large-scale, one-step preparation of the final material; in addition, particle size control can be achieved by controlling solution concentration, Factors such as nozzle droplet size. The material prepared by OLJACA and others through this method has a discharge specific capacity of 167mAh/g at 0.2C, and a discharge specific capacity of 137mAh/g at a high rate of 10C.

2.6 New roasting methods such as infrared and microwave

Compared with traditional resistance heating, new electromagnetic heating such as infrared and microwave can greatly shorten the high-temperature baking time and prepare carbon-coated composite cathode materials in one step.

HSIEH et al. used a new infrared heating roasting technology to prepare ternary materials. First, nickel cobalt manganese lithium acetate was mixed evenly with water, then a certain concentration of glucose solution was added, and the powder obtained by vacuum drying was roasted at 350°C for 1 hour in an infrared box. After roasting at 900°C (under N2 atmosphere) for 3 hours, the carbon-coated 333 composite cathode material was prepared in one step. SEM showed that the particle size of the material was around 500nm, with slight agglomeration. The X-ray diffraction (XRD) spectrum showed that the material had good The layered structure; in the voltage range of 2.8~4.5V, 1C discharges for 50 cycles, the capacity retention rate is as high as 94%, the first cycle discharge specific capacity reaches 170mAh/g (0.1C), 5C is 75mAh/g, and the high rate performance needs to be improve.

HSIEH et al. also tried medium-frequency induction sintering technology, using a heating rate of 200°C/min to prepare 333 materials with particle sizes evenly distributed between 300 and 600nm in a short time (900°C, 3h). The material has excellent cycle performance, but The high-rate charge and discharge performance needs to be improved.

As can be seen from the above, although the solid-phase method has a simple process, the material morphology and particle size are difficult to control; the co-precipitation method can prepare electrochemical products with narrow particle size distribution and high tap density by controlling temperature, stirring speed, pH value, etc. Ternary materials with excellent performance, but the co-precipitation method requires filtration, washing and other processes, producing a large amount of industrial wastewater; the stoichiometric ratio of material elements obtained by the sol-gel method, spray pyrolysis method and template method is precise and controllable, and the particles are small and dispersed. The materials have good properties and battery performance, but these methods have high preparation costs and complicated processes.

Sol-gel has a large environmental pollution, and the spray pyrolysis waste gas needs to be recycled and processed. The preparation of new excellent and cheap template agents needs to be developed; new infrared and medium frequency heating technologies can shorten the high-temperature roasting time, but the heating and cooling rates are difficult to control, and the material rate Performance could be improved. If methods such as spray pyrolysis, template method, and sol-gel can further optimize the synthesis process and use cheap raw materials, they are expected to achieve large-scale industrial application.
3. Problems with nickel-cobalt-manganese ternary cathode materials and their modifications

Compared with lithium iron phosphate and lithium cobalt oxide, nickel-cobalt-manganese ternary materials have the advantages of moderate cost and high specific capacity. However, there are also some problems that urgently need to be solved. The main problems include: low electronic conductivity, poor high-rate stability, and high voltage. Poor cycle stability, mixed cations (especially nickel-rich ternary), poor high and low temperature performance, etc. To address these problems, these problems are currently mainly improved through element doping and surface coating.

3.1 Ion doping modification

Incorporating trace amounts of other elements into the LiNixCoyMnzO2 lattice such as: Na, V, TI, Mg, Al, Fe, Cr, Mo, Zr, Zn, Ce, B, F, Cl can improve the electron density of the ternary nickel, cobalt and manganese. And ionic conductivity, structural stability, reduce the degree of cation mixing, thereby improving the electrochemical performance of the material. Ion doping can be divided into cation doping and anion doping.

3.1.1 Cation doping

Cation doping can be divided into equivalent cation doping and non-equivalent cation doping.

Equivalent cation doping can generally stabilize the material structure, expand ion channels, and improve the ion conductivity of the material. GONG et al. mixed Ni1/3Co1/3Mn1/3(OH)2 prepared by coprecipitation with LiOH and NaOH and then calcined it at high temperature to prepare Li0.95Na.