Brief analysis of ternary materials for lithium batteries -Lithium - Ion Battery Equipment
Nickel cobalt manganese is widely used because of its high specific capacity, long cycle life, low toxicity and low cost. Nickel is an important component in the redox energy storage of cathode materials for lithium ion batteries. How to effectively improve the specific capacity of materials by increasing the nickel content in materials is one of the current research focuses.
1 High nickel ternary material
Generally speaking, ternary cathode materials with high nickel mean that the mole fraction of nickel in the materials is greater than 0.6. Such ternary materials have the characteristics of high specific capacity and low cost, but also have the defects of low capacity retention rate and poor thermal stability.
The properties of the materials can be effectively improved by improving the preparation process. The properties of high nickel ternary cathode materials are largely determined by the micro nano size and morphology of particles. Therefore, the current important preparation method is to uniformly disperse different raw materials and obtain nanospheres with large specific surface area through different growth mechanisms.(Lithium - Ion Battery Equipment)
Among many preparation methods, the combination of coprecipitation method and high temperature solid phase method is the mainstream method at present. First, coprecipitation method is used to obtain precursor with uniform mixture of raw materials and uniform particle size, and then calcine at high temperature to obtain ternary materials with regular surface morphology and easy process control, which is an important method for industrial production at present.
The process of spray drying is simpler than that of coprecipitation, the preparation speed is faster, and the morphology of the obtained materials is no less than that of coprecipitation, which has the potential for further research. The mixed cation discharge and phase transition in charge discharge process of high nickel ternary cathode materials can be effectively improved by doping and coating modification. While inhibiting the occurrence of side reactions and stabilizing the structure, improving the conductivity, cycle performance, magnification performance, storage performance and high temperature and high pressure performance will still be the research focus.
2 Lithium rich ternary materials
All of this material has the characteristics of high voltage, and the mechanism of the first charge and discharge is different from that of the subsequent charge: the first charge will cause structural changes, which are reflected in two different platforms with 4.4V as the boundary on the charging curve. During the second charge, the charging curve is different from the first one. Because Li2O is irreversibly separated from the layered Li2MnO3 during the first charge, The platform 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 coprecipitation method, among which coprecipitation method is the most widely used method, and 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.
The future research directions of this material are as follows:
(1) The lack of understanding of the mechanism of lithium deinterlacation can not explain the phenomenon that the coulomb efficiency of materials will be low and the material performance will vary greatly;
(2) The study of doping elements is not enough and simple;
(3) The cathode material is eroded by electrolyte under high voltage, resulting in poor cycle stability;
(4) There are few commercial applications, and the investigation on security performance is not comprehensive enough. 3 Single crystal ternary cathode material
Under high voltage, as the number of cycles increases, the secondary particles or agglomerated single crystals may be pulverized at the primary particle interface or separated from the agglomerated single crystals at the later stage, resulting in greater internal resistance, faster battery capacity degradation and worse cycles.
Single crystal high voltage ternary materials can improve the lithium ion transfer efficiency and reduce the side reaction between materials and electrolyte, thus improving the cycling performance of materials under high voltage. First, ternary material precursor was prepared by coprecipitation method, and then single crystal LiNi0.5Co0.2Mn0.3O2 was obtained under the use 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 whole battery after 1300 cycles is still 98% of the initial discharge capacity. It is a ternary positive electrode composite with excellent electrochemical performance.
The cathode material production line is the first large-scale production of micron single crystal particle modified spinel lithium manganate and nickel cobalt lithium manganate ternary cathode materials in the world, reaching an annual production capacity of 500 tons.
4 Graphene doping
Graphene has a two-dimensional structure with a single atomic thickness, which is stable and has a conductivity of 1 times; 106S/m。 Graphene has the following advantages when used in lithium ion batteries: ① good conductivity and thermal conductivity, which is helpful to improve the rate performance and safety of batteries; ② As for graphite, graphene has more lithium storage space, which can improve the energy density of batteries; ③ The particle size is micro nano scale, and the diffusion path of lithium ion 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 carbonate based electrolytes currently used commercially, 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 severe oxidative decomposition, which leads to the failure of the lithium insertion and removal reaction of the battery. The development and application of new high-voltage electrolyte systems or high-voltage film forming additives to improve the stability of electrode/electrolyte interface is an effective way to develop high-voltage electrolytes. In the energy storage system, ionic liquids, dinitriles and sulfones are important organic solvents as the electrolytes of high voltage ternary materials. Ionic liquids with low melting point, nonflammable, low vapor pressure and high ionic conductivity show excellent electrochemical stability and have been widely studied.
A new solvent with high pressure stability can effectively improve the oxidation stability of electrolyte by completely or partially replacing the commonly used carbonate solvent. Moreover, 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. However, most of the new solvents have poor reduction stability and high viscosity, leading to the reduction of the cycle stability of battery cathode materials and the battery rate performance.
In high voltage electrolyte, film forming additives are also indispensable components, such as tetraphenyl phosphine ammoniate, LiBOB, lithium difluorodioxalate borate, tetramethoxy titanium, succinic anhydride, trimethoxyphosphorus, etc.
A small amount (<5%) of film forming additive is added to the carbonate based electrolyte to make it take precedence over the solvent molecules in the oxidation/reduction decomposition reaction, and an effective protective film is formed on the electrode surface, which can inhibit the subsequent decomposition of the carbonate based solvent. The film formed by the additives with excellent performance can even inhibit the dissolution of metal ions in the positive material and the deposition of metal ions in the negative electrode, thereby significantly improving the stability of the electrode/electrolyte interface and the cycling performance of the battery.
6 Surfactant assisted synthesis
The performance of ternary cathode material depends on the preparation method. Coprecipitation method is used to prepare the ternary cathode material. Through the synergistic use of surfactant, ultrasonic vibration and mechanical stirring, the prepared sheet precursor and lithium carbonate are finally annealed at high temperature to grow into a ternary layered structure, which is a new type of ternary cathode material synthesis process currently used.
It is found that using OA and PVP as surfactants can prepare hexagonal nano sheet cathode material precursors with excellent morphology, and the particle size distribution of the resulting nano sheet is relatively uniform, with a size of about 400 nm. The surfactant has a good shape control function on the precursor. The specific capacity of the assembled battery for the first discharge at 1C discharge rate is 157.093 mAh ˙ G-1, the capacity retention rate is more 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, coprecipitation method and sol gel method all need to be sintered at high temperature for several hours, which consumes large energy and has complex preparation process. Microwave heating is the volume heating caused by the dielectric loss of materials in the electromagnetic field. The heating speed is fast and uniform. The synthesized materials often have more excellent structure and performance, which is a very potential way to synthesize cathode materials.
The structure, micro morphology and electrochemical properties of the synthesized materials were characterized by XRD, SEM and charge discharge. The experimental results show that the cathode material synthesized in 1300W output power microwave has a specific discharge capacity of 185.2mAh/g for the first time, a coulomb efficiency of 84%, and a capacity of 92.3% (2.8~4.3V) after 30 cycles at 0.2C charge discharge condition, showing good electrochemical performance and application potential. 8 Infrared synthesis method
When the infrared ray irradiates the heated object, when the wavelength of the emitted infrared ray is consistent with the absorption wavelength of the heated object, the heated object absorbs the infrared ray, and the molecules and atoms inside the object resonate, causing strong vibration and rotation. Vibration and rotation increase the temperature of the object, so as to achieve the purpose of heating.
This heating principle can be used to prepare ternary cathode materials. HSIEH uses a new infrared heating roasting technology to prepare ternary materials. First, nickel cobalt manganese lithium acetate is mixed evenly with water, then glucose solution of a certain concentration is added, the powder obtained by vacuum drying is calcined in an infrared oven at 350 ℃ for 1h, and then calcined in a nitrogen atmosphere at 900 ℃ for 3h. Carbon coated 333 ternary cathode materials are prepared in one step. Within the voltage range of 2.8~4.5V, discharge at 1C for 50 cycles, and the capacity retention rate is as high as 94%, The specific discharge capacity of the first coil is 170 mAh/g, and the 5C is 75 mAh/g. The large 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.
It is 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. Mix the nickel cobalt manganese oxide and lithium carbonate evenly, and then put them into the plasma generator. Under the condition of oxygen, react at 600 ℃ for 20~60 minutes to obtain ternary cathode material Li (Ni1/3Co1/3Mn1/3) O2.
The prepared cathode material has a high initial discharge specific capacity of 218.9mAh ˙ G-1. At the same time, the cycle stability, magnification and high temperature performance are also due to the materials prepared by traditional methods.
Preparation of ternary cathode materials from waste batteries
The cost of cathode materials of lithium-ion batteries accounts for 30% - 40%. Therefore, the cost of lithium-ion batteries can be greatly reduced by recycling waste battery cathode materials and recovering the energy storage performance of cathode materials through preparation processes. Moreover, a complete lithium-ion battery industry chain should include the recycling of lithium-ion batteries.
Greenmea invested 100 million yuan to build the largest production line for the treatment of waste batteries and battery materials in China, recycling more than 4000 tons of cobalt resources annually, accounting for more than 30% of China's strategic cobalt resource supply, forming a characteristic recycling route for Greenmea's battery materials from waste batteries to new batteries.
The whole production line is made of nickel, cobalt and manganese recycled from waste batteries to prepare a solution, add synthetic agent, and through a series of processes, it becomes the cathode material of nickel cobalt manganese ternary power lithium ion battery. Since it was put into operation in October 2014, the output value has reached nearly 200 million yuan, and it is estimated that the output value can reach 500 million to 600 million yuan in the future.
1 High nickel ternary material
Generally speaking, ternary cathode materials with high nickel mean that the mole fraction of nickel in the materials is greater than 0.6. Such ternary materials have the characteristics of high specific capacity and low cost, but also have the defects of low capacity retention rate and poor thermal stability.
The properties of the materials can be effectively improved by improving the preparation process. The properties of high nickel ternary cathode materials are largely determined by the micro nano size and morphology of particles. Therefore, the current important preparation method is to uniformly disperse different raw materials and obtain nanospheres with large specific surface area through different growth mechanisms.(Lithium - Ion Battery Equipment)
Among many preparation methods, the combination of coprecipitation method and high temperature solid phase method is the mainstream method at present. First, coprecipitation method is used to obtain precursor with uniform mixture of raw materials and uniform particle size, and then calcine at high temperature to obtain ternary materials with regular surface morphology and easy process control, which is an important method for industrial production at present.
The process of spray drying is simpler than that of coprecipitation, the preparation speed is faster, and the morphology of the obtained materials is no less than that of coprecipitation, which has the potential for further research. The mixed cation discharge and phase transition in charge discharge process of high nickel ternary cathode materials can be effectively improved by doping and coating modification. While inhibiting the occurrence of side reactions and stabilizing the structure, improving the conductivity, cycle performance, magnification performance, storage performance and high temperature and high pressure performance will still be the research focus.
2 Lithium rich ternary materials
All of this material has the characteristics of high voltage, and the mechanism of the first charge and discharge is different from that of the subsequent charge: the first charge will cause structural changes, which are reflected in two different platforms with 4.4V as the boundary on the charging curve. During the second charge, the charging curve is different from the first one. Because Li2O is irreversibly separated from the layered Li2MnO3 during the first charge, The platform 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 coprecipitation method, among which coprecipitation method is the most widely used method, and 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.
The future research directions of this material are as follows:
(1) The lack of understanding of the mechanism of lithium deinterlacation can not explain the phenomenon that the coulomb efficiency of materials will be low and the material performance will vary greatly;
(2) The study of doping elements is not enough and simple;
(3) The cathode material is eroded by electrolyte under high voltage, resulting in poor cycle stability;
(4) There are few commercial applications, and the investigation on security performance is not comprehensive enough. 3 Single crystal ternary cathode material
Under high voltage, as the number of cycles increases, the secondary particles or agglomerated single crystals may be pulverized at the primary particle interface or separated from the agglomerated single crystals at the later stage, resulting in greater internal resistance, faster battery capacity degradation and worse cycles.
Single crystal high voltage ternary materials can improve the lithium ion transfer efficiency and reduce the side reaction between materials and electrolyte, thus improving the cycling performance of materials under high voltage. First, ternary material precursor was prepared by coprecipitation method, and then single crystal LiNi0.5Co0.2Mn0.3O2 was obtained under the use 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 whole battery after 1300 cycles is still 98% of the initial discharge capacity. It is a ternary positive electrode composite with excellent electrochemical performance.
The cathode material production line is the first large-scale production of micron single crystal particle modified spinel lithium manganate and nickel cobalt lithium manganate ternary cathode materials in the world, reaching an annual production capacity of 500 tons.
4 Graphene doping
Graphene has a two-dimensional structure with a single atomic thickness, which is stable and has a conductivity of 1 times; 106S/m。 Graphene has the following advantages when used in lithium ion batteries: ① good conductivity and thermal conductivity, which is helpful to improve the rate performance and safety of batteries; ② As for graphite, graphene has more lithium storage space, which can improve the energy density of batteries; ③ The particle size is micro nano scale, and the diffusion path of lithium ion 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 carbonate based electrolytes currently used commercially, 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 severe oxidative decomposition, which leads to the failure of the lithium insertion and removal reaction of the battery. The development and application of new high-voltage electrolyte systems or high-voltage film forming additives to improve the stability of electrode/electrolyte interface is an effective way to develop high-voltage electrolytes. In the energy storage system, ionic liquids, dinitriles and sulfones are important organic solvents as the electrolytes of high voltage ternary materials. Ionic liquids with low melting point, nonflammable, low vapor pressure and high ionic conductivity show excellent electrochemical stability and have been widely studied.
A new solvent with high pressure stability can effectively improve the oxidation stability of electrolyte by completely or partially replacing the commonly used carbonate solvent. Moreover, 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. However, most of the new solvents have poor reduction stability and high viscosity, leading to the reduction of the cycle stability of battery cathode materials and the battery rate performance.
In high voltage electrolyte, film forming additives are also indispensable components, such as tetraphenyl phosphine ammoniate, LiBOB, lithium difluorodioxalate borate, tetramethoxy titanium, succinic anhydride, trimethoxyphosphorus, etc.
A small amount (<5%) of film forming additive is added to the carbonate based electrolyte to make it take precedence over the solvent molecules in the oxidation/reduction decomposition reaction, and an effective protective film is formed on the electrode surface, which can inhibit the subsequent decomposition of the carbonate based solvent. The film formed by the additives with excellent performance can even inhibit the dissolution of metal ions in the positive material and the deposition of metal ions in the negative electrode, thereby significantly improving the stability of the electrode/electrolyte interface and the cycling performance of the battery.
6 Surfactant assisted synthesis
The performance of ternary cathode material depends on the preparation method. Coprecipitation method is used to prepare the ternary cathode material. Through the synergistic use of surfactant, ultrasonic vibration and mechanical stirring, the prepared sheet precursor and lithium carbonate are finally annealed at high temperature to grow into a ternary layered structure, which is a new type of ternary cathode material synthesis process currently used.
It is found that using OA and PVP as surfactants can prepare hexagonal nano sheet cathode material precursors with excellent morphology, and the particle size distribution of the resulting nano sheet is relatively uniform, with a size of about 400 nm. The surfactant has a good shape control function on the precursor. The specific capacity of the assembled battery for the first discharge at 1C discharge rate is 157.093 mAh ˙ G-1, the capacity retention rate is more 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, coprecipitation method and sol gel method all need to be sintered at high temperature for several hours, which consumes large energy and has complex preparation process. Microwave heating is the volume heating caused by the dielectric loss of materials in the electromagnetic field. The heating speed is fast and uniform. The synthesized materials often have more excellent structure and performance, which is a very potential way to synthesize cathode materials.
The structure, micro morphology and electrochemical properties of the synthesized materials were characterized by XRD, SEM and charge discharge. The experimental results show that the cathode material synthesized in 1300W output power microwave has a specific discharge capacity of 185.2mAh/g for the first time, a coulomb efficiency of 84%, and a capacity of 92.3% (2.8~4.3V) after 30 cycles at 0.2C charge discharge condition, showing good electrochemical performance and application potential. 8 Infrared synthesis method
When the infrared ray irradiates the heated object, when the wavelength of the emitted infrared ray is consistent with the absorption wavelength of the heated object, the heated object absorbs the infrared ray, and the molecules and atoms inside the object resonate, causing strong vibration and rotation. Vibration and rotation increase the temperature of the object, so as to achieve the purpose of heating.
This heating principle can be used to prepare ternary cathode materials. HSIEH uses a new infrared heating roasting technology to prepare ternary materials. First, nickel cobalt manganese lithium acetate is mixed evenly with water, then glucose solution of a certain concentration is added, the powder obtained by vacuum drying is calcined in an infrared oven at 350 ℃ for 1h, and then calcined in a nitrogen atmosphere at 900 ℃ for 3h. Carbon coated 333 ternary cathode materials are prepared in one step. Within the voltage range of 2.8~4.5V, discharge at 1C for 50 cycles, and the capacity retention rate is as high as 94%, The specific discharge capacity of the first coil is 170 mAh/g, and the 5C is 75 mAh/g. The large 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.
It is 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. Mix the nickel cobalt manganese oxide and lithium carbonate evenly, and then put them into the plasma generator. Under the condition of oxygen, react at 600 ℃ for 20~60 minutes to obtain ternary cathode material Li (Ni1/3Co1/3Mn1/3) O2.
The prepared cathode material has a high initial discharge specific capacity of 218.9mAh ˙ G-1. At the same time, the cycle stability, magnification and high temperature performance are also due to the materials prepared by traditional methods.
Preparation of ternary cathode materials from waste batteries
The cost of cathode materials of lithium-ion batteries accounts for 30% - 40%. Therefore, the cost of lithium-ion batteries can be greatly reduced by recycling waste battery cathode materials and recovering the energy storage performance of cathode materials through preparation processes. Moreover, a complete lithium-ion battery industry chain should include the recycling of lithium-ion batteries.
Greenmea invested 100 million yuan to build the largest production line for the treatment of waste batteries and battery materials in China, recycling more than 4000 tons of cobalt resources annually, accounting for more than 30% of China's strategic cobalt resource supply, forming a characteristic recycling route for Greenmea's battery materials from waste batteries to new batteries.
The whole production line is made of nickel, cobalt and manganese recycled from waste batteries to prepare a solution, add synthetic agent, and through a series of processes, it becomes the cathode material of nickel cobalt manganese ternary power lithium ion battery. Since it was put into operation in October 2014, the output value has reached nearly 200 million yuan, and it is estimated that the output value can reach 500 million to 600 million yuan in the future.
