Analysis and Latest Research on Preparation Technology of Lithium Battery Ternary Materials

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2019-10-10 14:33

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Analysis and Latest Research on Preparation Technology of Lithium Battery Ternary Materials

Basic Knowledge and Present Situation of 1. Ternary Materials

Common lithium ion cathode materials are generally embedded compounds.Includes:Layered structure of lithium cobalt oxide, spinel structure of lithium manganese oxide and olivine structure of lithium iron phosphate.The development of a cathode material system with high redox potential and output voltage, high reversible charge-discharge specific capacity, good electronic and ionic conductivity, and good cycle stability is an important research content in the field of lithium-ion batteries.

The ternary nickel cobalt manganese material generally refers to the lithium nickel cobalt manganese oxide LiNi1-x-yCoxMnyO2.The material has a ternary synergistic effect, and its electrochemical performance is better than any single material. It combines the cycle stability of LiCoO2, the high specific capacity of LiNiO2, and the advantages of LiMn2O4 thermal stability, safety and low price.

Increasing the nickel content in the ternary nickel-cobalt-manganese material can improve the reversible lithium insertion capacity of the material.However, the phenomenon of cation mixing is prone to occur, and with the increase of nickel content, the more serious the nickel-lithium mixing of the material, the irreversible capacity loss of the material.The introduction of cobalt can improve the electronic conductivity of the material, weaken the ion mixing phenomenon, stabilize the layered structure of the material, and improve the rate and cycle stability of the material.Reasonable adjustment of the proportion of ternary materials to optimize the performance of ternary materials is the research hotspot and focus in the field of lithium ion electrochemical.

At present, according to the ratio of nickel, cobalt and manganese, the commercial ternary material product models range from 111 ternary materials to 424, 523, 622, 811 ternary materials, and even higher nickel content.With the increase of nickel content, the energy density of the battery is also improved.

Among them, the 111 type material is the most mature material in the market at present due to the easy control of the preparation process and the use environment.The 622 product series has a higher energy density. With the increasing maturity and stability of its production process, 622 products have entered the stage of industrial application.811 products still need to continue research and development, and no battery manufacturers have yet put into large-scale commercial applications. This is because the nickel content is too high and the alkalinity is too high, and there are great difficulties in material preparation and use.

Factors Affecting the Electrochemical Properties of 2. Cathode Materials

There are many factors that affect the electrochemical performance of cathode materials. In addition to the crystal structure of the material itself, there are the following factors:crystallinity, particle size size distribution, stoichiometry, etc.

The lithium ion battery realizes the conversion of electric energy and chemical energy through the insertion and extraction reaction of Li between the positive and negative electrodes.The higher the degree of reversibility of Li intercalation and deintercalation and the smaller the influence on the host structure, the better the cycling performance of the material.The better the development of the crystal structure of the cathode material, that is, the higher the crystallinity, the more conducive to Li diffusion, the better the electrochemical performance of the material.On the contrary, the crystallization performance is not good or contains impurity relative material electrochemical performance influence is bigger.

Different morphology and particle size distribution will affect the tap density and compaction density of the material, and determine the volume energy density of the material.In general, the larger the particle size of the material, the smaller the tap density, and the smaller the specific surface area, the more unfavorable the Li extraction and embedding in the material.Therefore, controlling the microscopic morphology and particle size of the material can improve the performance of the ternary material.

The stoichiometric ratio and uniform distribution of nickel-cobalt-manganese ternary materials have a great influence on the synthesis and electrochemical properties of the materials.The in-depth study of the ratio of nickel, cobalt and manganese is of decisive significance for the preparation of materials with stable electrochemical properties.The deviation of the stoichiometric ratio and the uneven distribution of elements will lead to the appearance of heterophasic phases in the material.In addition to the above factors, the residual alkali, pH, single crystal particle size, lithium salt type, moisture, impurities, etc. of the ternary material also have a great influence on the electrochemical performance of the material.

Preparation method of 3. ternary material

The microstructure, particle morphology and electrochemical properties of cathode materials are closely related to the preparation method of the materials.Ni-Co-Mn ternary materials and LiCoO2 belong to the layered structure.Therefore, the preparation of ternary materials also mostly follows the preparation method of LiCoO2, mainly high temperature solid phase method, co-precipitation method, sol-gel method (sol-gel) and spray drying synthesis method.

1 High temperature solid phase method

High temperature solid state method is the most commonly used method for the preparation of metal oxides.The so-called solid phase method generally refers to the solid compound as raw material according to the stoichiometric ratio of mixed evenly, in a certain atmosphere and temperature roasting for a period of time, to obtain the desired sample method.Among them, the microstructure and electrochemical properties of the products are determined by factors such as the degree of mixing uniformity of raw materials, roasting time, temperature rise and fall rate, atmosphere and temperature stability.

Solid-phase synthetic materials have the characteristics of low equipment requirements, simple process, easy operation, mature process, low cost and large output.The biggest disadvantage of this method is that the quality of the material is difficult to control, including the particle morphology, composition and size of the material, resulting in poor consistency, stability and reproducibility of electrochemical performance.

Xu et al. Ni(OH)2 and Li2CO3 as raw materials, with an excess of 10% lithium, 750 degrees Celsius oxygen atmosphere sintering 12h to get LiNiO2.The button half cell was prepared by using active material, small particle conductive carbon black and polyvinylidene fluoride according to the mass ratio of 8:1:1. The test voltage range was between 2.7V and 4.3V, the first discharge specific capacity was 205 mAh/g, the first discharge efficiency was 84.7, and the cycle performance was good.

2 Co-precipitation method

The co-precipitation method, also known as the liquid phase method, is based on a precipitation reaction.Generally, salt solution of one or more metal ions is used as raw material, and the precipitate is produced by co-current reaction under the action of precipitant and complexing agent. After filtration, washing and drying, the product or precursor is obtained, and the positive electrode material is obtained after solid mixing with lithium salt and calcination in a certain temperature and atmosphere for a certain period of time.

Co-precipitation method has the advantages of accurate reaction measurement, low reaction temperature, simple operation, easy control of conditions, good reproducibility and stable electrochemical performance, and has become the most important method for commercial synthesis of the material.However, in the process of co-precipitation, the concentration of reactants, temperature, pH value, feeding rate and stirring rate determine the particle size, element distribution, crystal type and other physical parameters of the material.Therefore, it is necessary to strictly control the process parameters.

Li et al. used high-temperature solid-state reaction to prepare ternary layered oxides LiNi0.5Co0.2Mn0.3O2 with good spherical particles.With Ni0.5Co0.2Mn0.3(OH)2 and Li2CO3 as raw materials, the amount of lithium is 1.06.The sintering treatment scheme is to obtain the sample after pre-sintering at 500 ℃ for 5h and sintering at 960 ℃ for 12h in air atmosphere.

Hua et al. prepared Ni1/3Co 1/3Mn 1/3(OH)2 precursors with layered structure by mixed hydroxide co-precipitation.The effects of pH control on particle structure, morphology, particle size distribution and tap density were investigated.The split (006, 102) and (108, 110) characteristic peaks in the X-ray diffraction spectroscopy test results indicate that the material has a layered structure.Transmission electron microscopy results show that the (001) crystal plane is the preferred orientation during the co-precipitation reaction.The electrochemical performance test results show that the layered structure of the precursor determines the electrochemical performance of LiNi1/3Co 1/3Mn 1/3O2.

3 Sol-gel method

The sol-gel method takes the metal organic salt or inorganic salt solution as the raw material, and undergoes hydrolysis, condensation and other reactions under the action of complexing agent to form a metastable sol system. Under the action of aging and other conditions, the sol forms a gel with relatively fixed solid particles. After drying, the gel removes the solvent to obtain a xerogel with uniform distribution of metal ions with developed spatial structure. Heating removes the residual organic impurities in the xerogel system, the desired target product is then prepared by heat treatment.

The product prepared by this method has the advantages of uniform chemical composition, high purity, narrow and uniform particle size distribution, low heat treatment temperature, and precise control of the stoichiometric ratio.However, the disadvantages of this method are also obvious, including:The morphology of the product is difficult to control, the cost is high, the operation is complicated, and the industrialization is difficult.This method is currently limited to laboratory studies.

Luo et al. used sol-gel method to uniformly mix the raw materials according to the stoichiometric ratio (Li:Ni:Co:Mn = 1.05:0.5:0.2:0.3) with LiAc · 2H2O, Co(Ac)2 · 4H2O, Ni(Ac)2 · 4H2O, Mn(Ac)2 · 4H2O as raw materials and citric acid as complexing agent. Water bath heating removes the moisture in the sol to obtain a gel, after the colloid was dried at 450 ℃ for 5h in air atmosphere, the LiNi0.5Co0.2Mn0.3O2 material was synthesized by sintering at 900 ℃ for 12h in air atmosphere, and then modified by double-sided coating.Under the condition of 55 ℃, the voltage range is 2.5~4.5V, the first discharge specific capacity of 1C is 116.6 mAh/g, and the capacity retention rate of 50 cycles is 74.2, which shows excellent electrochemical cycle performance compared with the sample before modification treatment.

Zuo et al. used a sol-gel method to produce LiNi1/3Co 1/3Mn 1/3O2 with a layered structure.The effects of subsequent heat treatment temperature and time on the crystal structure, microstructure and electrochemical properties of the material were studied by XRD, scanning electron microscopy and charge-discharge test.The sample sintered at 700 ℃ for 2h has a good layered a-NaFeO2 structure, the specific discharge capacity is 169.2 mAh/g, and the capacity retention rate is 89.2 at 0.1C in the voltage range of 2.8~4.4V.

4 Spray drying method

Spray drying method refers to the metal soluble salt mixture in the drying chamber atomization to form small droplets, droplets in the form of spray contact with hot air, through evaporation, precipitation, decomposition, sintering and other processes to obtain a dry product.

This method has the advantages of less material powder agglomeration, good and uniform morphology, good dispersion of particle monomer and high tap density.Because of the advantages of high degree of automation, short preparation cycle and no industrial wastewater, spray drying is regarded as a production method of ternary materials with very broad application prospects.

Piskin et al. used nickel nitrate, cobalt nitrate, manganese nitrate and citric acid as raw materials to prepare precursors with good performance by ultrasonic spray pyrolysis. After heat treatment at 800, 900 and 1000 ℃, LiNi1-x-yCoxMnyO2 cathode materials with primary particle size in the range of 0.2 ~ 0.6μm (x is 0.2~0.06) were obtained.In the voltage range of 2.75~4.25V and 0.1C, the initial discharge specific capacity of the prepared LiNi1/3Co 1/3Mn 1/3O2 material is 188 mAh/g, and the discharge specific capacity is 180.5 mAh/g after 30 cycles, and the retention rate is 86%, indicating that the material has good cycle performance.

Kim et al. spray pyrolyzed the raw materials and sintered them in a box furnace at 900 ℃ for 20h to obtain LiNi1/3Co 1/3Mn 1/3O2.At a current density of 0.2mA/cm2, the first discharge specific capacity was 204 mAh/g.

In addition to the above methods, there are Pechini methods, hydrothermal synthesis methods, ion exchange methods, irradiated gel polymerization methods, microwave synthesis methods, spontaneous combustion methods, pulsed laser deposition, chemical vapor deposition methods, and the like.Different preparation methods have a great influence on the mixing degree and physical properties of the materials, and each has its own advantages and disadvantages in the synthesis of ternary materials.Because some methods have some defects in some aspects, such:The product has poor cycle performance or low capacity, the production process pollutes the environment, and the cost is high, so it is not suitable for large-scale industrial production, and these methods need to be improved.

Description:Article Sourcelithium battery alliance;The views in this article are for sharing and communication only. If copyright and other issues are involved, please inform us and we will deal with them in time.

In 2019, the demand for lithium batteries for light vehicles will reach 4515MWh

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