3.2v 100ah lifepo4 battery.Research on high-nickel ternary cathodes: Nuggets of ternary precursors, giants are forming

Research on high-nickel ternary cathodes (2): Nuggets of ternary precursors, giants are forming ternary precursors that directly determine the core chemical properties of ternary cathode materials. The ternary precursor is a key material for the production of the ternary cathode. It is mixed and sintered with the lithium source to form the ternary cathode. Its performance directly determines the core chemistry of the ternary cathode material.

Research on high-nickel ternary cathodes (2): Nuggets of ternary precursors, giants are forming

The ternary precursor directly determines the core chemical properties of the ternary cathode material. The ternary precursor is a key material for the production of the ternary cathode. The ternary cathode is made by mixing and sintering with the lithium source. Its performance directly determines the core chemical properties of the ternary cathode material. The specific performance is as follows: 1) The precursor impurities will be brought into The cathode material affects the cathode impurity content; 2) The particle size and particle size distribution of the precursor directly determine the particle size and particle size distribution of the ternary cathode; 3) The specific surface area and morphology of the ternary precursor directly determine the specific surface area of the ternary cathode , morphology; 4) The ternary precursor element ratio directly determines the ternary cathode element ratio, etc. The physical and chemical properties such as particle size, morphology, element ratio, and impurity content of the ternary cathode will affect the core electrochemical properties of lithium batteries such as energy density, rate performance, and cycle life. In addition, the application and promotion of new cathode materials such as gradient and core-shell structure ternary cathodes depend on the research and development breakthroughs of corresponding precursors.

The ternary precursor process is complex, and product consistency and magnetic foreign matter control are key. The most common synthesis method of the ternary precursor is the co-precipitation method, which is generated by nickel sulfate, cobalt sulfate, manganese sulfate and sodium hydroxide through a salt-alkali neutralization reaction under the protection of ammonia water as a complexing agent and a nitrogen atmosphere. Its core process Parameters include salt-alkali concentration, ammonia concentration, reaction liquid addition rate to the reactor, reaction temperature, pH value, stirring speed, solid content, etc. Each parameter will affect the precursor particle size, morphology, element ratio, etc. , so the control accuracy of process conditions is the key to determining product consistency, and it can also better reflect the process level of each company. As the ternary cathode develops towards single crystals and high nickel, the corresponding precursors are also developing towards small particle sizes and high nickel. The synthesis of small particle sizes has a short particle growth cycle, making it more difficult to control the morphology and particle size, and requires higher The precision of process parameter control; while high-nickel ternary materials have much higher requirements for the content of magnetic foreign matter than ordinary ternary materials, which require process transformation, workshop transformation, equipment research and development, and refined management of the entire production process to achieve this. The level of control can also better reflect the level of each company's technology.

The concentration of ternary precursors continues to increase, and the bargaining power of the industrial chain is strong. According to statistics, the domestic ternary precursor CR3 concentration increased steadily from 37.70% to 46.80% from 2016 to 2018. During the same period, the ternary cathode CR3 concentration dropped slightly from 32.41% to 30.51%. We believe this also reflects the highly customized nature of ternary precursors. Only companies that master core process technologies can win customer recognition. This has led to the polarization of the precursor industry, with leading companies’ production capacity exceeding demand and increasing concentration. Under the background that the existing ternary cathode materials are still dominated by ternary 5 series and 6 series products, the barriers to the subsequent mixed lithium sintering process are relatively low, resulting in relatively stronger business homogeneity, and the improvement of concentration needs to be 811, NCA The promotion of high-grade nickel ternary cathodes can be achieved by widening the technological gap between enterprises. The difference in concentration also leads to better bargaining power of precursor companies than cathode companies. Currently, the average gross profit margin of precursor companies is higher than that of cathode companies.

The demand side continues to benefit from the high growth rate of power batteries, and the high-end production capacity on the supply side is in short supply. We estimate that the global demand for ternary precursors will reach 358,600 tons, 495,900 tons, and 682,300 tons respectively from 2019 to 2021, with year-on-year increases of 98,700 tons, 137,300 tons, and 186,400 tons respectively, with year-on-year growth rates reaching 38.0% respectively. , 38.3%, 37.6%. According to statistics, domestic ternary precursor and ternary cathode production in 2018 were 218,000 tons and 136,800 tons respectively. Since domestic ternary cathodes are currently mainly supplied to domestic lithium battery companies, assuming that domestic ternary cathode production accounts for 50% of global production, it is estimated that Global ternary cathode production and ternary precursor production reached 273,600 tons and 259,900 tons respectively. Domestic ternary precursor production accounted for 84% of the global share, occupying a dominant position in the global supply chain. As ternary materials develop towards single crystal, high nickel, and new structures, the demand for precursors will continue to shift to high-end, and companies that master core technologies are expected to continue to maintain their leading position.

Recommended targets: Recommend GEM, the absolute leader in ternary precursors in the world, pay attention to Guangdong Bangpu, a subsidiary of CATL, as well as A-share listed companies Huayou Cobalt and Dow Technologies, etc.

Risk warning: New energy vehicle sales growth is less than expected, battery prices have dropped beyond expectations, and new cathode material technology has been iterated.

Table of contents

1. What is the ternary precursor?

The ternary precursor material is nickel cobalt manganese hydroxide, with the chemical formula NixCoyMn(1-x-y)(OH)2. It is an important upstream material for the production of ternary cathode materials. It uses lithium carbonate with lithium sources (NCM333, NCM523, NCM622 , NCM811, NCA (lithium hydroxide) are mixed and then sintered to obtain the finished ternary cathode. Ternary cathode materials are one of the key materials for making lithium batteries. Their downstream terminals include new energy vehicles, energy storage, power tools, and 3C electronic products.

The production of ternary precursors is highly customized, with different combinations of element ratios, morphologies, particle sizes, etc. According to particle size, precursors can be divided into small particle precursors, medium particle precursors, and large particle precursors. Generally, the particle size of small particle precursors is distributed between 3 and 5 microns. Due to the temperature required in the mixed lithium sintering step, Relatively low, due to cost considerations, it is mostly used to produce single crystal ternary cathode materials that require higher sintering temperatures (with the same element ratio and particle size, the sintering temperature of single crystal ternary cathodes is 100~200 higher than that of ordinary types. degree); medium particle precursors are generally between 6 and 8 microns; large particle precursors are generally above 10 microns, and the mixed lithium sintering step requires a higher temperature. From a cost perspective, it is generally used to make polycrystalline/diodes. Subspherical ternary cathode material. According to the molar ratio of elements, the precursors can be divided into type 111, type 523, type 622, type 811 and NCA type, or high nickel type and low nickel type.

2. The synthesis process of ternary precursor is complex

The main process of ternary precursor production is shown in the figure. The main raw materials include nickel sulfate, cobalt sulfate, manganese sulfate and sodium hydroxide. In order to avoid the oxidation of metal ions, the entire precursor preparation process needs to be carried out under the protection of inert gas nitrogen. . The main processes include:

1) Pretreatment: Configure salt into a mixed salt solution of a certain concentration, prepare sodium hydroxide into an alkali solution of a certain molar concentration, and use a certain concentration of ammonia as a complexing agent;

2) Reaction: Add the filtered and impurity-free salt solution, alkali solution, and complexing agent to the reactor at a certain flow rate, and react under appropriate reaction conditions to generate ternary precursor crystal nuclei and gradually grow;

3) Post-processing: When the particle size reaches the predetermined value, the reaction slurry is filtered, washed, and dried to obtain the ternary precursor.

The precursor production process can be divided into two types: batch method and continuous method. During the reaction process of the intermittent method, the reaction slurry continuously overflows through the overflow pipe to the concentrator for concentration. The clear liquid is filtered out for wastewater treatment, and the material is returned to the reactor to allow the crystals to continue to grow until the particle size of the precursor in the reactor reaches requirements, then transfer to the aging kettle and let it sit for a period of time to improve the crystal structure and morphology of the precursor, and then enter the subsequent filtration, washing, drying, and packaging processes. In the continuous law, during the reaction process, materials are fed and discharged at the same time. The reaction slurry continuously overflows into the aging kettle through the overflow pipe. After aging and standing, it then enters the subsequent filtration, washing, drying, and packaging processes.

The particle size distribution of the precursor produced by the batch method is extremely narrow, and the production capacity of the continuous method is higher. The residence time of materials produced by the batch method in the reactor is relatively uniform, and the particle size distribution of the produced precursor is narrower. It is suitable for the production of high-end products such as high-nickel and single-crystal precursor products; however, it has the disadvantages of poor production continuity and poor batch stability. . The production yield of the continuous method is higher. The production capacity of the continuous method of the same volume reactor is about twice that of the batch method, and the batch stability is good. However, due to the simultaneous feeding and discharging of materials, the residence time distribution of the materials in the reactor is wide. , the particle size distribution of the produced precursor is also wider, especially there are some particles with too small particle size, which will cause over-burning during the cathode sintering process, thereby affecting the quality of the cathode. It is currently mainly used to produce mid-to-low-end precursor products.

The process parameters that need to be controlled during the reaction include: concentration of salt and alkali, ammonia concentration, the rate at which salt solution and alkali solution are added to the reactor, reaction temperature, pH value of the reaction process, stirring rate, reaction time, solid content of the reaction slurry, etc. . The process parameters mentioned above are discussed separately below.

Ammonia concentration

When there is no complexing agent such as ammonia water, adding a precipitant will cause violent nucleation and growth, forming loose secondary particles with low tap density. In this way, it is difficult to grow precursors with uniform particle size and high tap density. As a complexing agent, ammonia can effectively complex the added metal ions, which not only slows down the disturbance of the precipitation balance caused by the addition of raw materials, controls the supersaturation of the precipitates in the solution, but also reduces the speed of nucleation and growth, making the crystals slow. Growth is easy to control.

The higher the ammonia concentration, the better. Excluding cost and pollution factors, the specific surface area and tap density will show a parabolic change pattern as the ammonia concentration changes:

(1) When the concentration of ammonia water is low, there are fewer metal ions to complex, resulting in higher supersaturation, and the growth rate is too fast, resulting in small primary particle size, many gaps, loose and porous particle morphology, and poor density.

(2) When the concentration of ammonia water is high, the primary particles can grow thicker, and these thicker grains will again cause more gaps and increase the specific surface area.

In addition, the main function of ammonia as a reaction complexing agent is to control free metal ions by complexing metal ions. If the dosage of complexing agent is too much or too low, the ratio of nickel, cobalt, and manganese in the precursor will deviate from the designed value. , and the complexed metal ions will be drained away with the supernatant, causing waste and causing greater difficulties in subsequent wastewater treatment. Therefore, the concentration of ammonia water required to prepare ternary precursors of different compositions is also different.

Ammonia water affects the performance of precursors, cathodes, and lithium batteries mainly by affecting the element ratio and particle morphology:

1) Too high ammonia concentration will cause the primary particles in the precursor agglomerate to be too large, resulting in more gaps between materials, resulting in an excessively large specific surface area of the precursor; too low ammonia concentration will cause the precursor crystal to grow too fast and reduce the sphericity. It becomes worse and there are more gaps between materials, resulting in an excessively large specific surface area of the precursor.

2) The specific surface area of the precursor is too large, resulting in the specific surface area of the positive electrode generated after sintering being too large. On the one hand, the positive electrode tap and compaction density decreases, and the energy density of the lithium battery decreases. At the same time, the interface reaction between the positive electrode material and the electrolyte intensifies, and the battery The cycle life is reduced; on the other hand, due to the increase in gaps and the increase in lithium ion transmission channels, the battery rate performance is improved.

3) In addition, deviations in ammonia concentration will cause an imbalance in the element ratio in the precursor, and changes in nickel content will be inherited into the cathode material, thereby affecting the energy density of lithium batteries.

pH value

The pH during the precipitation process directly affects the nucleation and growth of crystal particles. The reason why precursor particles with different morphologies are obtained under different pH conditions can be explained by the influence of precipitation pH conditions on the crystal nucleation rate and growth rate. When the pH value is low, due to the small supersaturation in the solution, the growth rate of the precursor particles is greater than its nucleation rate, and it is easy to obtain particles with better morphology. Under high pH conditions, the supersaturation in the solution system is large, the formation rate of crystal nuclei is very fast, and the growth rate of precursor particles is slow, thus forming a microcrystalline structure with smaller particles.

The pH value of the reaction process directly affects the morphology and particle size distribution of the precursor. By adjusting the pH value, the morphology of primary grains and secondary particles can be controlled:

The pH value is low: it is conducive to the growth of crystal nuclei, and the primary crystal grains are thicker and larger; the secondary particles are prone to agglomeration, causing the secondary balls to become abnormally shaped.

High pH value: It is conducive to the formation of crystal nuclei. The primary crystal grains are flake-shaped and appear very small; the secondary particles are mostly spherical.

At the same time, the pH value can also be appropriately adjusted during the reaction process so that the same secondary spherical particle has primary crystal grains with different morphologies. As shown in the figure, there are some fine grains on the surface of the secondary sphere formed by the agglomeration of the later primary grains. These fine grains are formed by raising the pH value at the end of the reaction.

The PH value affects the performance of the precursor, cathode, and lithium battery mainly by affecting the element ratio and particle morphology:

1) If the PH is too high, the nucleation speed of the precursor crystal will be too fast, and the primary particles will be small and dense, but the secondary particle size distribution will be broadened; if the PH is too low, the nucleation speed will be too slow, and crystal nucleation growth will dominate. As a result, the primary particles in the precursor agglomerate are too large, and the agglomerates between secondary particles increase, resulting in more gaps between materials, resulting in an excessively large specific surface area of the precursor.

2) Excessive specific surface area of the precursor will lead to a decrease in the tapping and compaction density of the positive electrode, and a decrease in the energy density of the lithium battery. At the same time, the interface reaction between the positive electrode material and the electrolyte will be intensified, and the battery cycle life will be reduced; on the other hand, due to the increase in voids, lithium There are more ion transmission channels and the battery rate performance is improved. The broadening of the precursor particle size distribution will lead to over-burning of some small particle precursors in the mixed lithium sintering step, resulting in a decline in the quality of the finished cathode.

3) In addition, deviations in the pH value will cause an imbalance in the element ratio in the precursor, and changes in nickel content will be inherited into the cathode material, thereby affecting the energy density of lithium batteries.

temperature reflex

Temperature mainly affects the rate of chemical reactions. In the reaction of the precursor, the nucleation and growth rate become faster as the temperature increases. However, if the temperature is too high, it will cause oxidation of the precursor, uncontrollable reaction process, changes in the structure of the precursor, etc. Keep the temperature as high as possible.

The influence of precipitation temperature on precursors is mainly reflected as follows:

(1) The increase in temperature will cause the rate of precipitation growth to change. The nucleation and growth rates both increase with the increase in reaction temperature. That is, the increase in reaction temperature will lead to an increase in the reaction rate, thereby triggering growth. Speed up.

(2) In the reaction system, the dissolution of insoluble crystals and the precipitation of ions coexist. The equilibrium point can be expressed by the solubility product, and the solubility product increases with the increase of temperature, that is, the higher the temperature, the reaction will move towards The solid dissolution direction shifts, making precipitation difficult. In addition, the crystallization process of the hydroxide precursor is an exothermic process, so the nucleation reaction will be inhibited as the temperature increases, and crystal growth will dominate.

(3) If the temperature is too high, it will aggravate the volatilization of ammonia in the system and reduce the ammonia concentration of the system. The result is consistent with the reduction of ammonia concentration, which will reduce the metal complexation amount of the system and is not conducive to growth.

(4) When the temperature is too low, the solubility product (Ksp) is low, which causes the reaction to favor nucleation. At the same time, the diffusion rate of ions and molecules is low, which will slow down the growth of the precursor. If the stirring is not sufficient at this time, it will also cause the feed to The local metal ion concentration in the mouth is too high, causing local explosive nucleation.

Temperature that is too high or too low is detrimental to nucleation and growth. Only a certain temperature is most beneficial to nucleation and growth.

Temperature affects the conduction of precursors, cathodes, and lithium battery performance mainly by affecting particle morphology and crystal structure:

1) If the temperature is too high, the growth of the precursor crystal will become dominant and the nucleation will become secondary, resulting in primary crystal growth.