Development status of China's power lithium-ion battery industry
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Basic knowledge of power lithium-ion battery

Development status of China’s power lithium-ion battery industry

The industry is gaining momentum. The formation of China’s lithium-ion battery industry began in the late 1990s. Affected by the rapid development of industries such as mobile communications, China has now become the world’s second largest producer of lithium-ion batteries. In 2009, China’s output of lithium-ion batteries exceeded 1.5 billion, with sales reaching 17 billion yuan. The country has invested a lot of financial and material resources in the research and development of power-type lithium-ion batteries. The 863 plan has set up major special projects for electric vehicles. With strong support for the research and development of key materials and batteries for power lithium-ion batteries, research and development institutions such as the Institute of Physics of the Chinese Academy of Sciences, Beijing Research Institute of Nonferrous Metals, Institute of Mechanical Sciences, and the 18th Research Institute of China Electronics Technology Group Corporation have integrated key technologies for power battery systems. , Significant progress has been made in research on key components and products.

At present, China’s under-construction power lithium-ion battery capacity exceeds 4.5 billion wh. If calculated at 30 kW per vehicle, it can meet the loading requirements of 150,000 vehicles. The main production companies include BYD Co., Ltd., Tianjin Lishen Battery Co., Ltd., Shenzhen BAK Battery Co., Ltd., Chery Automobile Co., Ltd., CITIC Guoan Mengguli Power Technology Co., Ltd., Wanxiang Group Co., Ltd., Shanshan Investment Holding (Group) Co., Ltd., etc., in addition to a large number of small and medium-sized enterprises.

China has formed a relatively complete power-type lithium-ion battery industry chain, but the core components are still monopolized by advanced foreign companies. At this stage, the positive and negative materials, electrolyte (electrolyte), etc. of various battery products have basically completed localization, but core materials such as battery separators and lithium hexafluorophosphate are still monopolized by several companies such as Japan and the United States. Although some progress has been made in diaphragm and lithium hexafluorophosphate technology recently, the industry is still small and still dominated by low-end products. The development of the lithium-ion battery industry has entered a critical stage of industrialization, promotion and application.

①Policy support is a three-pronged approach. In recent years, the Ministry of Science and Technology, the Ministry of Industry and Information Technology, and the State-owned Assets Supervision and Administration Commission have respectively issued programs such as “National Major Special Projects for the Industrialization of Electric Vehicles in the Twelfth Five-Year Plan”, “Energy-saving and New Energy Vehicle Industry Development Plan” and “State-owned Enterprise Pure Electric Vehicle Investment Plan” to support With the development of the new energy automobile industry, the power-type lithium-ion battery industry has ushered in a golden opportunity for rapid development.

②Manufacturing enterprise. At present, there are more than 300 companies engaged in lithium-ion batteries in China. Among them, the companies that are committed to the research and development of power-type lithium-ion batteries and have been mass-produced are mainly Tianjin Lishen Battery, BYD, BAK Battery, Wanxiang Electric Vehicle, and CITIC Guoanmeng Guli, Shanshan Technology, etc.

Company name: Tianjin Lishen Battery Co., Ltd.: Founded in 1997, it is mainly engaged in the research and development, production and sales of lithium-ion battery technology. It has an annual production capacity of 500 million Ah lithium-ion batteries. The products are used in portable mobile electronic devices, New energy electric vehicles, wind and solar power generation, energy storage systems and other fields.

In the 11th Five-Year “863” plan, the subject of “High-performance Lithium-ion Power Battery System for Electric Vehicles” was undertaken, mainly focusing on the integration and testing of large-capacity lithium-ion power batteries, as well as related accessories such as battery casings, gaskets, and safety valves. There are fewer patents involving core technologies.

Company name: BYD Co., Ltd.: Founded in 1995, China’s only enterprise that masters the large-scale production technology of lithium iron phosphate battery packs for vehicles. The self-developed “iron battery” has been successfully applied to BYD’s pure electric vehicle E6 and hybrid power Get on the F3DM. The annual output of dual-mode electric vehicles is 1,200. Due to battery capacity limitations, only 100 vehicles are shipped every month.
Applied for 32 related patents, mainly focusing on the preparation of battery cathode materials such as lithium manganate and lithium iron phosphate and battery integration, as well as the preparation of electrolytes (electrolytes) and separators, involving the key components of power-type lithium-ion batteries, which belong to the core technology patent.

Company name: Shenzhen BAK Battery Co., Ltd.: Founded in 2001, it is one of the world’s largest manufacturers of lithium-ion battery cells with a daily production capacity of about 1.5 million. The products cover IT communication fields such as mobile phones, digital, notebooks, and electric In power battery fields such as tools, electric bicycles, and electric cars, three power lithium-ion battery cells have been introduced.

Company name: Chery Automobile Co., Ltd.: Its subsidiary Chery New Energy Vehicle Technology Co., Ltd. was established in 2010 and is responsible for the research and development of clean energy vehicle technologies such as hybrid vehicles and alternative fuel vehicles.
Application for 16 power lithium-ion battery patents, mainly for the integration, detection, and control of automotive power lithium-ion batteries, lithium-ion battery management systems, and lithium-ion battery recycling.

Company name: Wanxiang Electric Vehicle Co., Ltd.: Founded in 2002, it is a wholly-owned subsidiary of Wanxiang Group, dedicated to the research and development, production and sales of clean energy, energy-saving and environmentally friendly vehicles.
Undertook the topic of “Research and Development of Pure Electric Passenger Vehicle Power System Platform Technology”, a major project of energy-saving and new energy vehicles in the Eleventh Five-Year “863” plan, focusing on the development of polymer lithium-ion power batteries. Applied for 13 power-type lithium-ion battery patents, the patent content mainly covers the integration of polymer lithium-ion power batteries, the preparation of lithium manganate battery materials, and the battery pack management system.

Company name: CITIC Guoan Mengguli (MGL): MGL was established in 2000. The investor is CITIC Guoan Group, a subsidiary of China CITIC Group, which is divided into Power Technology Co., Ltd., Power Technology Co., Ltd., and New Energy Technology Co., Ltd. . The main products are lithium cobalt oxide, lithium manganese oxide cathode materials and power lithium ion secondary batteries. Its large-capacity lithium manganese oxide power battery is the exclusive product for the 2008 Beijing Olympics pure electric buses. Applied for 11 power-type lithium-ion battery patents, mainly covering the preparation of lithium manganate cathode materials, battery integration and battery modules.

Company name: Shanshan Investment Holding (Group) Co., Ltd.: Shanghai Shanshan Technology Co., Ltd. was established in 1999, which is mainly engaged in the research, development, production and operation of lithium-ion battery materials. 10 companies, with products covering lithium-ion battery cathodes, anodes, electrolytes (electrolytes), separators, aluminum shells, and related raw materials and resource products, etc. China’s electrolytes (electrolytes) have the second largest market share, and anode materials (graphite) ) The market share is the first, and it is the supplier of negative electrode materials for BENZ pure electric vehicles, American pure electric vehicles Miles and German BMW pure electric vehicles.
Applied for 12 patents for power-type lithium-ion batteries. Each subsidiary of the patent content has its own focus. Among them, Changsha Shanshan Power Battery (a subsidiary of Shanghai Shanshan Technology) is mainly an iron phosphate lithium ion battery, and Shanghai Shanshan Technology is mainly for preparation Lithium-ion battery anode materials, Dongguan Shanshan battery materials mainly develop electrolytes (electrolytes), and Hunan Shanshan new materials are used to prepare lithium manganate and lithium iron phosphate cathode materials.

Current status of power lithium-ion battery industry
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Basic knowledge of power lithium-ion battery

Current status of power lithium-ion battery industry

(1) Industrial chain composition
The manufacturing of power batteries has undergone four steps: battery materials, batteries, battery modules, and battery packs, and its industrial chain constitutes

  1. Preparation of raw materials: cathode materials, anode materials, electrode substrates, separators, electrolytes, etc.
  2. Cell manufacturing: electrode plate production, cell packaging, charging and discharging testing, safety performance testing, etc.
  3. Battery pack integration: battery module grouping, battery pack performance testing, battery pack safety protection, battery management system, etc.
  4. Terminal applications: electric vehicles, electric bicycles, electric tools, high-power appliances, etc.

(2) Current status of industry development
From the report Analysis of the Global Hybrid Electric and Electric Vehicle Lithiur-ion Battery Market released by Frost&Sullivan in June 2012, it can be seen that in 2010, the market competition of lithium-ion batteries for vehicles The number of ion battery companies has reached more than 35, with a total revenue of 500 million US dollars. Among them, the main factors affecting competitive performance are battery cost, vehicle performance, technology, reliability, partnerships, and customer relationships. Application terminals mainly include hybrid electric vehicles, pure electric vehicles and plug-in electric vehicles.

In 2010, the world’s top 5 lithium-ion battery manufacturers were South Korea’s LG Chem, with a market share of 17.6%; Japan’s AESC with a market share of 16.3%; Japan’s Panasonic with a market share of 11.4%; and the United States’ A123 with a market share of 11.4%. Share 8.7%; and SB LiMotive, a joint venture between Germany and South Korea, with a market share of 5.4%. These 5 companies contributed 59.4% of the market’s sales share.

In 2010, the global hybrid and electric vehicle market revenue reached 502 million U.S. dollars. Among them, South Korea’s LG Chemical’s revenue was 883 billion U.S. dollars, Japan’s AESC was 818 billion U.S. dollars, Panasonic’s was 572 billion U.S. dollars, and the U.S. A123 system was 437 billion U.S. dollars. SB LiMotive, a joint venture between Germany and South Korea, has revenues of US$272.1 billion. The combined revenue of the five companies accounted for nearly half of the total market revenue, and they are the main suppliers for the production of lithium-ion batteries for electric vehicles.

Among the top seven automotive lithium-ion battery manufacturers in the world in 2012, 1 was a US company, and the remaining 6 were companies in Asian countries, including 4 Japanese companies and 2 South Korean companies. The power lithium-ion battery manufacturers with a market share of more than 10% are South Korea’s LG Chem, accounting for 19.4%; Japan’s AESC, accounting for 19.4%, and Japan’s Yuasa, accounting for 13.8%. The 47th place is respectively Panasonic 8.3%, Johnson Controls 4.4%, Hitachi Vehicle Energy 4.4%, and Samsung SD 12.2%.

As a result of maintaining good relations with automakers, South Korea’s LG Chem has become the current market leader. In addition to the production of lithium-ion batteries, it also provides various other auto parts, and is chosen by many manufacturers as the battery supplier. For example, the main supplier of Chevrolet Volt is LG Chem. Nissan enjoys a good quality reputation in the electric vehicle and hybrid vehicle manufacturing industry. The exclusive battery supplier for its Leaf product is Japan’s AESC. The American A123 system has strong infrastructure construction. The company is located in the Detroit area close to the three major US automakers, and its geographical location is of important strategic significance.

(3) Analysis of market supply and demand
Benefiting from the market changes of hybrid vehicles and plug-in hybrid vehicles that used nickel-metal hydride batteries to gradually switch to using lithium-ion batteries, the demand for lithium-ion batteries for vehicles has seen rapid growth since 2011. According to CCID Consulting’s analysis, the global lithium-ion battery industry reached US$27.81 billion in 2013, and it will reach US$37.46 billion in 2014. Driven by the industrialization of new energy vehicles, the global lithium-ion battery industry reached 523.2 in 2015. One hundred million U.S. dollars.
From the perspective of market structure, within the lithium-ion battery industry, from 2013 to 2015, the proportion of power batteries will gradually increase. In 2014, lithium-ion power batteries accounted for 33.4% of the total internal total, and ordinary lithium-ion batteries accounted for 66.6%. By 2015, the proportion of the two will be closer, and the proportion of lithium-ion power batteries will rise to 49.2%. The proportion of ion batteries dropped to 50.8%.

Judging from the supply and demand status of China’s power-type lithium-ion battery materials, the supply and demand of lithium borate and lithium manganate in the positive electrode materials are balanced, and the supply of lithium iron phosphate is in short supply; the supply of negative electrode materials is sufficient and the competitive landscape is stable; the electrolyte (electrolyte) can be satisfied in China. However, the electrolyte lithium hexafluorophosphate relies on imports; the lithium-ion battery separator has not yet achieved localization, and basically depends on imports.

Classification and technological development of power lithium-ion
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Basic knowledge of power lithium-ion battery

Classification and technological development of power lithium-ion batteries

  1. Battery cell
    First, a special solvent and a binder are mixed with the powdered positive and negative active materials respectively, and the positive and negative materials are made into a slurry after being evenly stirred. Then, the positive and negative electrode slurry is uniformly coated on the surface of the metal foil by an automatic coating machine, and after automatic drying, the positive and negative electrodes are automatically cut into positive and negative electrode pieces. Secondly, according to the sequence of positive electrode sheet, diaphragm, negative electrode sheet, and diaphragm, the electrolyte is injected through winding, sealing, and positive and negative lug welding processes to complete the assembly process of the battery and make the finished battery cell. Finally, the finished battery is placed in a test cabinet for charging and discharging tests and aging, and qualified finished batteries are screened out.
  2. Battery pack
    The operating voltage of the battery pack is very high, and multiple lithium-ion batteries must be connected in series to reach the operating voltage of the car battery. At present, electric vehicles use lithium-ion batteries as power sources, which involves the assembly, structure, design, and management of lithium-ion battery packs.

As lithium-ion batteries are increasingly used in high-power equipment, the number of batteries in series and parallel is also increasing, which will increase the complexity of the battery management system, so it is necessary to improve the integration of the management system. Because the characteristics of different types of batteries are different, research on a more versatile battery management system (BMS) has become one of the key technologies for electric vehicles. In recent years, BMS has been greatly improved, but some parts are still not perfect, especially in terms of reliability of collected data, residual charge estimation (SOC) accuracy, fast charging of batteries, equalization circuits, and safety management. Improve and improve.

At present, some large foreign automobile manufacturers and battery suppliers have done a lot of research and experiments on various batteries, and have developed many battery management systems and installed them on vehicles for trial. The more representative ones are the BATTMAN system designed by B.Hauck in Germany, the battery management system on the EVI electric vehicle produced by General Motors in the United States, the Smart Guard system developed by Aerovironment in the United States, and so on.

  1. Lithium-ion battery classification (by application field)
    The lithium-ion battery industry is an energy storage industry, which is widely used in communication power supplies, electric vehicles, and megawatt-level energy storage power supplies (such as wind energy, solar energy, smart grid) and other fields. According to different application areas, lithium-ion batteries can be divided into electrical appliances batteries, energy storage batteries, power batteries and micro batteries.

Electrical appliances battery (high energy);
Application areas: electrical products such as information, communications, office and digital entertainment.
Features: fast updating of electrical appliances, constant power, low requirements for battery rate performance, operating temperature, cost, and cycle performance.
Performance: The battery energy density is higher than 200wh/kg, and 100% DOD is 200-300 times.

Energy storage battery (long life);
Application areas: small energy storage power supply: UPS, solar energy, fuel cell, wind power and other distributed independent power system energy storage.
Features: The requirements for battery power and energy density are not high, and the requirements for volume and weight are relatively low.
Performance: 0-20 years of service life, maintenance-free, stable performance, low price, better temperature characteristics and lower self-discharge rate.

Power battery (high power):
Application areas: all kinds of electric vehicles, electric tools, high-power appliances.
Features: It requires high power density, safety, temperature characteristics, low cost, and high self-discharge rate.
Performance: The current power density level is 800~1500wW/kg, and the target is above 2000 W/kg.

Micro battery:
Application areas: wireless sensors, micro unmanned aircraft, implantable medical devices, micro robots, etc.
Features: Electrical appliances are difficult to maintain, and require high stability and longevity.
Performance: Long life, good stability, all solid-state batteries are required.

  1. Technology Roadmap
    During the five years from 2010 to 2015, the electrode and electrolyte (electrolyte) technology of lithium-ion batteries did not change significantly. The current technology is still being developed. The cathode materials of lithium-ion batteries mainly include lithium titanate materials, nickel cobalt aluminum three Element materials, nickel diamond manganese ternary materials, lithium manganate materials, spinel structure manganese compounds and lithium iron phosphate. The negative electrode material will still be mainly graphite, and titanate materials will be developed at the same time. The electrolyte is made of flat lithium polymer and prismatic lithium ion materials.

In the five-year period from 2015 to 2020, the technology will undergo major changes on the original basis, and both electrode and electrolyte technologies will be greatly developed. Among them, for cathode materials, lithium titanate materials and nickel diamond aluminum ternary materials will gradually be eliminated from the market after 2015, while lithium manganese phosphate materials are expected to replace lithium iron phosphate materials. The development trend of the entire cathode materials is 2020 The cathode of lithium-ion batteries based on manganese element materials was realized in about a year. Graphite in the negative electrode material is still one of the main materials, but it is expected to be eliminated from the market around 2020, titanate will continue to be used, and it is expected to realize the preparation of negative electrodes using silicon-tin alloy and vanadium around 2020. . The electrolyte is expected to realize the preparation of an electrolyte using lithium hyperpolymer as a material around 2020 on the original basis.

Electrolyte and diaphragm of power lithium-ion battery
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Electrolyte and diaphragm of power lithium-ion battery

Electrolyte (electrolyte)
Electrolyte (electrolyte) is one of the important components of lithium-ion batteries. During the working process of a lithium ion battery, the electrolyte solution is filled in the space between the positive and negative electrodes and the separator, and plays the role of transmitting lithium ions and communicating the positive and negative electrodes. The electrolyte solution is essential to the safety and service life of the battery. Important.

In the conventional electrolyte (electrolyte) system, the organic solvent is mainly carbonate, and the lithium salt is mainly lithium hexafluorophosphate (LiPF6). Among them, carbonates mainly include cyclic carbonates (such as ethylene carbonate EC, propylene carbonate PC, etc.) and chain carbonates (such as dimethyl carbonate DMC, diethyl carbonate DEC, ethyl methyl carbonate EMC, etc.), General electrolyte (electrolyte) contains basic components such as EC and DEC. In addition, in order to improve the stability of the SEI film, VC, VEC and additives containing sulfur and boron are often added to the electrolyte (electrolyte); to prevent overcharging, additives such as biphenyl are often added; to improve safety, phosphate esters are added Class flame retardants and fluorine substitute solvents. According to the function, the electrolyte solution can be divided into high-power type, high-temperature type, low-temperature type, anti-overcharge type and high-capacity type, all of which are realized by adding corresponding additives.

Diaphragm
In the main raw materials of lithium-ion batteries, in addition to the positive and negative electrodes and electrolyte solutions, the separator is also a very important component. The main function of the diaphragm is to separate the positive and negative electrodes of the battery to prevent the positive and negative electrodes from contacting and short-circuit. In addition, the diaphragm also has the function of allowing electrolyte ions to pass through.

Lithium-ion battery separator materials mainly include polyolefins, polymer materials, and inorganic materials. According to the characteristics of raw materials and different processing methods, lithium-ion battery separators can be divided into polyolefin separators, polymer separators, ceramic separators, and fiber separators.

At present, polyolefin membranes are mainly polyethylene and polypropylene, including single-layer polyethylene (PE), single-layer polypropylene (PP), and three-layer PP/PE/PP composite films. At present, the preparation process of polyolefin membrane has two technical routes: dry method and wet method.

Polymer membranes are currently the most studied membrane. Compared with ordinary polyolefin membranes, polymer membranes have lower production process requirements, better electrochemical performance, abundant polymer raw materials, and low production costs. However, polymer films generally have poor mechanical strength, and their mechanical strength must be enhanced to adapt to mechanical automated production.

SEPARION diaphragm is a ceramic porous membrane composed of PET non-woven fabric as an organic support and a layer of inorganic ceramic oxide coating on its surface. The diaphragm has good thermal stability. Compared with polyolefin membranes, the safety performance is greatly improved, but the puncture strength of the membrane needs to be improved.

Nanofiber diaphragm is prepared by electrostatic spinning method, which is a new type of preparation method and preparation process of diaphragm material. In this method, under the action of a high-voltage electric field, the polymer material solution splits into countless nano jets at the tip of the spinneret and solidifies to form a polymer nanofiber membrane. The diaphragm has good thermal stability, but its industrialization is relatively complicated. Recently, this process is not very mature and has not yet been commercialized.

Composition of negative electrode material for power lithium-ion battery
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Basic knowledge of power lithium-ion battery

Composition of negative electrode material for power lithium-ion battery

As one of the main components of lithium-ion batteries, the negative electrode has a direct impact on and limits the electrochemical performance and application range of the battery system, such as the active components of the material, the size, morphology, and electrode composition of the active particles. At present, the anode materials used in lithium-ion batteries include carbon materials (graphite carbon materials, non-graphite carbon materials) anodes and non-carbon materials (alloy anodes and metal oxides) anodes. Non-graphite anode materials mainly include silicon (Si)-based materials, lithium titanate (Li4Ti5O12) and tin (Sn)-based materials.

Carbon/graphite material has a high theoretical specific energy (372mAh/g), is cheap and easy to obtain, and the preparation process is mature, so it is widely used. However, the first charge of the carbon/graphite negative electrode will form a solid electrolyte membrane (SEI) on the surface of the carbon particles, resulting in a loss of battery capacity, and the amount of solid electrolyte membrane (SEI) generated increases with the increase in the number of charge and discharge cycles, and the internal impedance of the battery increases. , The specific energy and power performance are reduced. The modification methods of graphite anode materials include surface oxidation, surface coating, element doping and so on. According to the type of coating material, surface coating includes surface carbon coating, metal and its oxide coating, polymer coating and so on. Carbon coating includes soft carbon coating and hard carbon coating (resin coating).

In theory, some metals or metalloids that can form alloys with lithium can be used as anode materials for lithium-ion batteries, such as Si, Ge, Sn, Pb, Al, etc. These materials are collectively referred to as alloy anode materials. Compared with graphite, the theoretical lithium storage capacity of alloy anode materials is large, and the lithium storage potential is low. The theoretical capacity of silicon (Si) is as high as 4200mAh/g, which is much higher than graphite and other carbon anode materials. It is the highest theoretical capacity among various alloy materials currently studied; the voltage of lithium insertion into silicon is lower than 0.5v, and the insertion process There is no co-intercalation of solvent molecules, which is very suitable as a negative electrode material for lithium-ion batteries. At present, the preparation methods of silicon materials mainly include chemical vapor deposition, vacuum evaporation, thermal spraying, and sputtering. However, in terms of process maturity, stability, controllability, efficiency and cost, magnetron sputtering technology is better than Other methods.

Lithium titanate (Li4Ti5O12) has a spinel structure. When used as a negative electrode material for lithium-ion batteries, it has a small volume change, a very stable structure, excellent cycle performance and a stable discharge voltage, and a higher electrode voltage. It is a raw material for preparation More abundant, and the price is cheap. However, the capacity is smaller than that of the carbon anode material, and the potential is too high relative to the metal lithium electrode. At present, the synthesis methods of lithium titanate (Li4Ti5O12) mainly include solid-phase reaction method and sol-gel method.

Development status of various anode materials:
Natural graphite: has been tried in batches
Advantages: mature technology and supporting process, low cost.
Disadvantages: the specific energy has reached the limit, the cycle performance and rate performance are poor, and the safety performance is poor.

Artificial graphite: has been applied in small batches
Advantages: mature technology and supporting process, good cycle performance.
Disadvantages: low specific energy, poor rate performance, and poor safety performance.

Mesocarbon microspheres: Has been used in batches
Advantages: mature technology and supporting processes, good rate performance, and good cycle performance.
Disadvantages: low specific energy, poor safety performance, and high cost.

Hard Carbon: Trial in small batches
Advantages: high reversible capacity, large capacity improvement space, good rate performance, and good safety performance.
Disadvantages: immature technology and supporting processes, low first-time efficiency, high cost, and poor processing performance.

Lithium titanate: Trial in small batches
Advantages: excellent rate performance, excellent high and low temperature performance, excellent cycle performance, and excellent safety performance.
Disadvantages: immature technology and supporting process, high cost, low specific energy.

Metal alloys: development stage
Advantages: high reversible capacity, large capacity improvement space, and good safety performance.
Disadvantages: immature technology and supporting processes, low first-time efficiency, high cost, poor processing performance, poor cycle performance and rate performance.

Cathode material composition of power lithium-ion battery
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Basic knowledge of power lithium-ion battery

Cathode material composition of power lithium-ion battery

During the charging and discharging process of lithium-ion power batteries, the positive electrode material not only provides the lithium required for the reciprocating insertion and extraction of the positive and negative lithium intercalation compounds, but also bears the burden of forming a solid electrolyte (electrolyte) interface film (SEI film) on the surface of the negative electrode material. Of lithium. The current cathode materials mainly include lithium cobalt oxide, lithium nickel oxide, lithium manganate, lithium iron phosphate and nickel cobalt manganese three-element materials.

Lithium cobalt oxide (LiCoO2) is a layered rock salt structure cathode material. Although it has shortcomings such as scarce resources and poor thermal stability, it is still the main source of small lithium ion secondary batteries due to its stable electrochemical performance and high reliability of production processes. Applied cathode material. The synthesis methods of lithium cobalt oxide (LiCoO2) mainly include solid-phase reaction method, sol-gel method, hydrothermal method, precipitation method and so on. There are significant differences in physical and electrochemical properties of lithium cobalt oxide (LiCoO2) materials synthesized by different methods. At present, commercial lithium cobalt oxide (LiCoO2) materials are mainly synthesized by high-temperature solid-phase reaction.

Lithium nickel oxide (LiNiO2) is similar in structure to lithium cobalt oxide (LiNiO2), with higher theoretical capacity, low price, large reserves and no pollution to the environment, but its internal structure leads to very harsh preparation conditions and relatively low cycle capacity attenuation Fast, its practical process has been relatively slow. The use of a small amount of other metal ions to replace part of the nickel to stabilize its structure is one of the directions for improving the performance of the material in recent years, mainly doped with elements such as cobalt (Co), magnesium (Mg) and aluminum (Al). The synthesis method of lithium nickelate (LiNiO2) is mainly a high-temperature solid-phase reaction method.

Lithium manganate (LiMn2O4) is a positive electrode material with a spinel structure. It is cheap and pollution-free, but its capacity decays severely at high temperatures, and the structure of manganese acid (LiMn2O4) is unstable during charging and discharging, due to the occurrence of Jahn-Teller The effect leads to a certain limit in the scope of application. The traditional synthesis methods of lithium manganate (LiMn2O4) mainly include solid-phase reaction method and liquid-phase reaction method. At present, some people use microwave heating method, pulsed laser deposition method, plasma lift chemical vapor deposition method and radio frequency magnetron jet method to prepare lithium manganate (LiMn2O4).

Lithium iron phosphate (LiFePO4) is an olivine-shaped cathode material that belongs to the orthorhombic system. It has a high theoretical capacity, good thermal stability, and excellent charge-discharge cycle performance at room temperature. Therefore, it has good performance in specific fields. Application prospects. However, due to the low energy density, low ionic conductivity and low electronic conductivity of the current materials, poor rate performance, poor low-temperature performance, and complex synthesis, etc., the material is used in power-type lithium-ion batteries, and a lot of work needs to be done. At present, the synthesis methods of lithium iron phosphate (LiFePO4) mainly include high-temperature solid-phase synthesis, microwave sintering, and sol-gel.

Nickel cobalt manganese ternary material (LiNixCo1-2xMnxO2) has excellent charge-discharge cycle stability and better safety performance, so it becomes another positive electrode material that can replace lithium cobaltate. Among them, the product with x=1/3 has the best comprehensive electrochemical performance, and it is also the most studied and the fastest-developing material. At present, the nickel diamond manganese ternary material (LiNixCo1-2xMnxO2) mainly realizes the mixing of Ni, Co, and Mn ions in the liquid phase, and then uses the precipitation method to prepare the reactants before the high temperature reaction. In addition, carbonic acid can also be used The salt precipitation method is used to synthesize the material.

At present, the mainstream cathode materials are lithium cobalt oxide, lithium manganate, ternary materials (lithium nickel manganese oxide) and lithium iron phosphate. Among them, the most mature and widely used lithium-ion battery cathode material is lithium cobalt oxide. However, due to its high cost and safety problems as a power battery, the research and development of power-type lithium-ion batteries in various countries focuses on manganese Lithium oxide, ternary materials and lithium iron phosphate: Lithium manganate technology is relatively mature, but its shortcomings are the short life of single cells and poor high temperature resistance; ternary materials are modifications of existing materials, and more attention is paid to the process Parameters: Lithium iron phosphate is favored because of its long cycle life, excellent safety performance, better high temperature performance, and extremely low price, but it also has poor electrical conductivity, poor low temperature resistance, poor rate performance, It is difficult to control the consistency of material batches and other shortcomings.

The working principle and structure of power lithium-ion battery
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Basic knowledge of power lithium-ion battery

The working principle and structure of power lithium-ion battery

(1) Working principle
Lithium-ion batteries are generally batteries that use lithium alloy metal oxide as the positive electrode material, graphite as the negative electrode material, and non-aqueous electrolyte. The charging and discharging process of lithium ion batteries is the process of intercalation and deintercalation of lithium ions. In the process of intercalation and deintercalation of lithium ions, it is accompanied by the intercalation and deintercalation of electrons equivalent to that of lithium ions (the positive electrode is usually represented by insertion or deintercalation, and the negative electrode is represented by insertion or deintercalation). In the process of charging and discharging, lithium ions are intercalated/deintercalated and intercalated/deintercalated back and forth between the positive and negative electrodes, which is vividly called the “rocking chair battery”

When the battery is charged, lithium ions are generated on the positive electrode of the battery, and the generated lithium ions move to the negative electrode through the electrolyte (electrolyte). The carbon as the negative electrode has a layered structure with many micropores. The lithium ions reaching the negative electrode are inserted into the micropores of the carbon layer. The more lithium ions are inserted, the higher the charging capacity. In the same way, when the battery is discharged (that is, during use of the battery), the lithium ions embedded in the carbon layer of the negative electrode are released and move back to the positive electrode. The more lithium ions returned to the positive electrode, the higher the discharge capacity.

(2) Battery composition
Lithium-ion batteries are generally composed of a positive electrode, a negative electrode, an electrolyte (electrolyte), a separator, and a casing. The common materials and the proportion of the cost.

positive electrode:
Lithium-inserting transition metal oxides: lithium cobalt oxide, lithium manganate, nickel diamond manganese composite materials, lithium iron phosphate: 40% to 46% of the total cost

negative electrode:
Lithium compounds with potential close to lithium potential: artificial graphite, natural graphite, graphitized carbon materials, graphitized mesophase carbon beads and metal oxides: 5% to 15% of the total cost

Electrolyte (electrolyte):
LiPF6 alkyl carbonate with polymer materials: ethylene carbonate (EC), propylene carbonate (PC) and low-viscosity diethyl carbonate (DEC), etc.: 5% to 11% of the total cost

Diaphragm:
Polyene microporous membrane: PE, PP or their composite membrane, PP/PE/PP three-layer diaphragm: 10%~14% of the total cost

shell:
Metal: steel, aluminum: 18%~36% of total cost