Current situation interpretation: core technology of power lithium battery

Lithium power website a few days ago, there are many domestic power battery industry news. First the SAIC joins power battery area and cooperates with Ningde, the second popular industry at home, the world's third largest power battery companies. They set up a power battery system company; it is said that BYD will split power battery department and supply for all car companies. It is reported that this action will change the global market. The consecutive annual production and sales volume of domestic electric car market keep the first in the world for two years. It is extended to more than 1 million cars, accounting for more than 50% of global market ownership. China becomes the top one on the electric car market overlooking America. The most important actions for electric car industry prospect and development is the improvement of power battery technology.

The development of electric cars need to be better batteries, power battery than energy, life, safety, and the price, is very important to the development of pure electric vehicles. Which has the advantages of high specific energy, long life lithium ion batteries is currently the most practical value of the electric car battery, in hybrid vehicles, pure electric vehicles and fuel cell vehicles are widely used. The current commercial power battery technology level and in the next 10 years is expected to reach the target as shown in figure 1, and often these indicators in actual production is contradictory, battery performance need to weigh the consideration. Aspires to the improvement of the performance of the battery electrode material, electrolyte, the performance of the diaphragm assembly technology at the same time, battery group and management technology of the follow up is also important. The purpose of this paper is to battery from the battery material technology, design and manufacturing technology and battery technology for lithium ion batteries as the core of the power battery development achievements, at the same time in the future!

Discussion: power lithium battery core technology development present situation

Figure 1 existing power battery and technical indexes of the next 10 years of development goals

1, lithium electric materials technology

Anode materials are

System of lithium-ion battery anode materials are very rich (figure 2), at present, the cobalt acid lithium, manganese acid lithium, lithium iron phosphate, lithium nickel manganese cobalt anode materials research has been mature. Cobalt acid lithium materials given a 200-210 ma · h/g, its true density and sheet material compaction density are the highest of the anode materials, existing commercial cobalt acid lithium/graphite system of charging voltage can improve 4.40 V, already can meet smart phones and tablets for high volume energy density of soft package requirements of the battery. Manganese acid lithium materials with low cost, simple production process, high thermal stability, good resistance to overcharge, high discharge voltage platform and high safety. Fit for low cost of light electric vehicle batteries, but the existence theory capacity is low, the cycle may be manganese element in the process of dissolution issues affecting the service life of the battery in high temperature environment. Domestic manganese acid lithium materials mainly to meet the mobile power supply, power tools and electric bicycle market demand, has to the trend of the development of the low end. Sliding ternary laminated battery anode materials are mainly applied in power type, except all accounts for one-third of the nickel, cobalt, manganese LiNi1/3 co1/3 mn1/3 O2 in the application of power battery is relatively mature, high capacity of LiNi0.5 Co0.2 Mn0.3 O2 also has entered the batch application, general mixed with manganese acid lithium is applied in electric vehicle battery. Nickel aluminum doped lithium cobalt oxide (NCA) energy density can be close to high voltage cobalt acid lithium batteriesIn recent years, the electric car manufacturer tesla this computer is used to drive electric vehicle batteries, the material can be mixed with manganese acid lithium used in the manufacture of automotive power battery, domestic NCA precursor has formed a stable production capacity, the further development of enterprise has completed the NCA cathode material, in process of product promotion. lithium iron phosphate batteries high safety, long service life, the power of the Nano materials and the fast development of ferromanganese lithium phosphate materials with high density, high energy and high power material performance stable, further reduce the cost, meet the demand of the domestic market step by step and the needs of the present stage of China's new energy cars, spinel lithium nickel manganese acid high voltage and high voltage ratio capacity rich lithium manganese anode material is still under development.

Discussion: power lithium battery core technology development present situation

Figure 2 lithium ion battery electrode material system

Anode materials

Can be used to power battery anode materials with graphite, hard/soft carbon and alloy material, graphite anode materials are widely used, the reversible capacity can reach 360 ma · h/g. Amorphous soft or hard carbon can meet the battery at a high rate and low temperature applications, start to application, but they are mainly mixed with graphite application. On anode materials for lithium titanate has the optimal ratio of performance and cycle performance, suitable for large current quick charge battery, but the production of low specific energy battery and high cost. Nano silica was introduced in the 1990 s that can be used for high capacity anode, by a small amount of Nano silicon doping to improve capacity of carbon anode materials is a hotspot of current research and development, adding a small amount of Nano silicon or silicon oxide anode materials have begun to enter the small batch application stage, the reversible capacity of 450 ma · h/g. But as a result of lithium embedded in silicon after its volume expansion, cycle life when in actual use will reduce the problems to be further solved.

The electrolyte

Lithium ion battery electrolyte with high dielectric constant commonly ring carbonate with low dielectric constant linear carbonate mixture. In general the electrolytes of lithium ion battery should meet high ionic conductivity (10-3 ~ 10-2 s/cm), low electronic conductivity, wide electrochemical window (0 ~ 5 v), thermal stability (- 40 ~ 60 ℃), and other requirements. Six fluoride phosphate lithium and other lithium salt, solvent refining, new electrolyte preparation, function additive technology continues to progress, it is the development direction of further improving its working voltage and the high and low temperature performance, improve the battery safe ionic liquid electrolyte and solid electrolyte are being developed.

The diaphragm

Polyolefin microporous membrane for its excellent mechanical properties, good electrochemical stability and the characteristic of the relatively cheap, are main varieties in the lithium ion battery diaphragm market [7].Including polyethylene (PE) monolayer film, polypropylene (PP) monolayer film and PP/PE/PP three-layer composite microporous membrane. Using dry process production of domestic manufacturers more, PE wet process diaphragm has more companies can be mass production. Widely with ceramic coating technology, resistance to high temperature and high voltage of the diaphragm will become the future research direction.

2, monomer battery technology

The basic design of the lithium-ion batteries still with SONY company released an application for a patent for the same in 1989, the shape of the monomer is cylindrical, rectangular metal shell (aluminum/steel) and square soft package in bulk, cylindrical battery is mainly used in notebook computers, tesla now companies such as selection of 18650 cylindrical batteries for electric cars. Square cell average amount is larger, batteries by volume rao, Z laminated, winding lamination, the anode coated laminated, laminated winding methods such as production. Cylindrical batteries, the most mature technology, the manufacturing cost is low, but the large cylindrical battery cooling ability is poorer, therefore, generally choose small cylindrical batteries. Automotive battery capacity big, cell number, management system is more complicated and expensive. Square battery winding structure in the production process is relatively simple, but for the most suitable for soft sheet battery, adopting except spinel cathode material and ternary material lithium iron phosphate batteries are available this method. High reliability, long life fold type battery suitable for all kinds of material system, general Volt plug-in hybrid cars and Nissan Leaf electric car batteries are manufactured lamination process. To 2015, the lithium iron phosphate monomer battery energy than 140 w. h/kg, ternary material mixed lithium manganese acid monomer battery energy than 180 w. h/kg, adopt the NCA small cylindrical battery than on international energy 240 w. h/kg, the next few years than lithium ion monomer battery energy will further enhance, expected in 2020 to a maximum of 300 w. h/kg.

3, battery system technology

From the commercialization of lithium ion power battery system point of view, the key core technologies including battery group technology (integrated cell group, thermal management, collision safety, electrical safety, etc.), battery management system (BMS), the precise measurement of the electromagnetic compatibility technology, signal (such as monomer voltage, current, etc.) technology, battery state estimate, battery equalization control technology, etc.

Discussion: power lithium battery core technology development present situation

Figure 3 simple power battery system diagram

The BMS and battery system of other key core components including sensor, controller, actuator and other components are basically by the automobile electronic technology monopoly power (Germany and Japan, the United States).Domestic currently part of the enterprise has successfully developed intelligent electric meter, current, voltage, insulation sensor can replace abroad. Affecting the popularization and application of the electric car is the primary factor of lithium ion power battery safety and use cost, in addition to the safety of the battery ontology, life, and to further improve consistency, modular technology, battery group technology (integrated cell group, thermal management, collision safety, electrical safety, etc.) also has more obvious gap with foreign. International car battery group technology is relatively mature at present, domestic research institutes in BMS the precise measurement of the electromagnetic compatibility technology, signal technology, battery state estimate, battery equalization control technology, etc, to carry out a thorough research.

Key technology research and development including the electric battery management comprehensive battery electrochemical model, electrical safety design, state estimation, balanced management, fault diagnosis and calibration, and charging management etc.The battery thermal management key technologies and system development should be designed according to the structure of the battery pack and battery production thermal calculation and analysis, research different thermal management technology of the cooling temperature effect, low cost, simple operation, safety and reliability of the battery thermal management cooling scheme. Root cell structure light weighting need to battery system and the related structure as the research object, considering the mutual coupling between features, from two aspects of optimization of structural design and material selection for structure vibration resistance, impact resistance and lightweight integrated optimization design of the key technology research. Linking to the parts material, structural design, design scheme is optimized, the battery safety in electrical, mechanical and thermal safety on the basis of the research on the safety of the battery system overall scheme design, for the battery prediction, thermal safety monitoring early warning system for fault diagnosis and prevention and control key technology.

4, looking

Quite a long period of time in the future, lithium ion battery is still the most applicable electric car batteries, lithium manganese acid anode materials, the anode material ternary system, lithium iron phosphate cathode material, composite carbon anode materials, ceramic coating membrane, electrolyte salts and functional electrolyte technology to support the development of battery technology progress and industrial development. Battery system technology in the application progress, safety and reliability will be improved further in the coming years.

The research of lithium ion power battery model and the relationship between model and parameter, the characteristics of battery pack, balanced strategy of efficient high-capacity lithium-ion battery pack, monomer battery charging and discharging thermal model and the battery pack temperature field analysis, research methods and control, optimization method for fast charge battery are come to be carried out. Power battery system should be redesign based on the product and upgrade the design according to the needs of the future automotive power battery manufacturing mode. Work hard on the basis power battery materials, battery manufacturing technology and system on the whole industrial chain at the same time, improve product quality, reduce the cost for mass production, and promote the competitiveness of the industry.

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