Comprehensive analysis of the development status and technical trends of cylindrical power lithium batteries

The general trend of electrification is becoming more and more intense. Through policy guidance and support, my country has become the world's largest new energy vehicle market. As we all know, the important bottleneck of new energy vehicles lies in the battery life. In this context, the state has issued the Action Plan for Promoting the Development of Automotive Power Batteries and the Roadmap for Energy-saving and New Energy Vehicle Technology to encourage the use of high-energy-density batteries. The recent Catalogue for the Guidance of Foreign Investment Industries (Revised in 2017) The policy proposes to lift restrictions on pure electric vehicle joint ventures and to remove restrictions on automotive electronics and power battery shares. This is also an important measure to promote the application of high energy density batteries in the new energy vehicle market. Based on policy inversion and the advancement of power battery technology itself, we analyze the product technology benchmarking model of ternary lithium and solid-state lithium batteries to deduce the future development pattern of power batteries.

1. Analysis of the status quo of power battery development

At present, domestic new energy vehicles are still using lithium iron phosphate (BYD-based) and ternary lithium batteries. The cruising range of the models can basically reach 300 kilometers, but the average energy density of the battery system is only 115Wh/Kg. In March 2017, the Ministry of Industry and Information Technology and other four ministries and commissions jointly promulgated the Action Plan to Promote the Development of Automotive Power Batteries, pointing out that by 2020, the specific energy of new lithium-ion power applications will exceed 300Wh/Kg; the specific energy of the system will strive to reach 260Wh /Kg.

The data shows that the current energy density of power batteries in my country differs from the target value by 126%. It is too difficult for lithium iron phosphate batteries to reach the target value in 2020, but it is completely possible for the ternary lithium battery represented by Tesla. Yes, the power battery used is good, and the efficiency of the BMS management system is also high; in addition, the solid-state lithium battery can also increase the energy density of the battery system to 260Wh/Kg.

1. Ternary lithium and lithium iron phosphate batteries-the current mainstay

At present, the global new energy vehicle market has entered a critical period of vigorous development, and mainstream auto companies have deployed new energy vehicles. Therefore, the rapid maturity of the lithium battery industry chain will further promote the large-scale application of new energy vehicles. From a global perspective, typical car companies' supporting models mainly use Japanese and Korean power batteries, mainly ternary lithium, and their cruising range basically reaches or exceeds 350 kilometers.

Table 1 Supporting situation of global mainstream power batteries

Looking at the country again, from the 2017 promotion catalog of the first six batches of new energy vehicles, the energy density of the batteries in the new models has also increased to varying degrees. In the first batch of catalogs, only 13.11% of the models with an energy density of over 115Wh/Kg accounted for only 13.11%. By the fifth batch of catalogs, this proportion reached 73%. It can be seen that the increase in power battery energy density is the general trend. The supporting power batteries of mainstream electric vehicle companies are also gradually transforming to ternary lithium, and the cruising range can basically reach the level of 300 kilometers.

Table 2 Supporting situation of domestic mainstream power batteries

Looking at the situation of new energy vehicles carried by power battery companies at home and abroad, the trend of ternary lithium batteries becoming the mainstream technology route has been irreversible, but there is still room for improvement in vehicle mileage. This is probably due to the low energy density of the power battery, and the room for improvement in BMS efficiency is still to be explored.

2. All-solid lithium power battery-the future development direction

The research and development goals of high-energy density lithium batteries successively formulated by countries around the world are actively deploying forward-looking technologies such as lithium-sulfur batteries, lithium-air batteries or lithium-metal batteries.

On the basis of inheriting the advantages of traditional lithium batteries, solid-state lithium batteries have greatly improved their safety and energy density. At present, the energy density that can be provided by the research and development of all-solid-state lithium batteries can basically reach 300~400Wh/kg, which is expected to become an important development direction of the next generation of high-energy-density power and energy storage battery technology. This has been the consensus of academia and industry.

Figure 1 The world's stage targets for power battery energy density

Figure 2 The trend of the world's lithium battery technology route

Global power battery related companies are also accelerating their deployment in the field of all-solid-state lithium batteries to seize the opportunity. At present, the industrialization process of each technology path is different. Among them, the polymer solid-state battery has developed rapidly. Due to its high-temperature working performance, the laboratory has been completed. It is verified that a small number of enterprises have realized small-scale industrialization.

Current status of R&D and application of solid-state lithium batteries (polymer solid-state batteries)

Bollore, France: All-solid-state secondary batteries (LMP), the anode material uses metal lithium, and the electrolyte uses polymer (PEO, etc.) films. It has been applied in batches in France’s EVs, shared service vehicles “Autolib” and small electric buses “Bluelus,” The total application exceeds 3000 vehicles.

United States Seeo: The all-solid secondary battery uses Daiso's dry polymer film. The sample battery pack provided has an energy density of 130-150Wh/kg. In 2017, the energy density can reach 300Wh/kg, and it has not been promoted and applied.

CATL: At present, a polymer battery cell with a capacity of 325 mAh has been designed and manufactured, which shows good high-temperature cycling performance and has not been promoted and applied.

Qingdao Institute of Energy, Chinese Academy of Sciences: The large-capacity solid-state polymer lithium battery "Qingneng I" has completed the deep-sea scientific research. Its energy density exceeds 250 Wh/kg, and its 500-cycle capacity remains above 80%. It maintains very good safety performance under severe test conditions such as pressure. "Qingneng II" has also been successfully developed, with an energy density of up to 300 Wh/kg, and has not yet been promoted and applied.

In addition, among solid-state lithium batteries, sulfide solid-state batteries (lithium-sulfur batteries) have huge development potential due to their high energy density and low cost. Toyota, Samsung, CATL, Toyota and other domestic and foreign companies have accelerated their deployment. Among them, Toyota's technology is the most advanced. Toyota launched sulfide solid-state batteries in 2010. In 2014, the energy density of its experimental prototype reached 400Wh/kg. As of the beginning of 2017, the number of Toyota solid-state battery patents reached 30, much higher than other companies. According to Toyota executives, Toyota may realize the industrialization of sulfide solid-state batteries in 2020. Domestic enterprise CATL is relatively leading in sulfide solid-state batteries, and is accelerating the development of sulfide all-solid-state lithium metal batteries for pure electric vehicles.

Research and development status of solid-state lithium batteries (sulfide solid-state batteries)

Toyota: Started to launch solid-state batteries in 2010, and its experimental prototype energy density reached 400Wh/kg in 2014.

Samsung Japan Research Institute: Trial-produced a 2000mAh, 175Wh/kg laminated all-solid secondary battery using sulfide-based solid electrolytes.

Sakti3 (U.S.): In 2015, it received an investment of 15 million U.S. dollars from British home appliance giant Dyson. The solid-state battery developed by it uses ceramics as the electrolyte, metal lithium or lithium alloy as the negative electrode, and the energy density reaches 1000Wh/L. It is still in research and development. stage.

Qingtao Energy: The company's core lies in the development and production of high-solid content ceramic diaphragms and inorganic solid electrolytes. At present, the team has cooperated with BAIC for a pilot test, which may be used as an important component of BAIC's electric vehicles in the future.

CATL: The main research and development direction is sulfide electrolyte. The positive electrode coating method is adopted to solve the problem of interface reaction. The hot pressing method reduces the interface resistance.

2. Comparison and impact analysis of the two technical routes

1. Ternary lithium battery: mature technology and currently occupy the mainstream of the market

From the perspective of product maturity, the American Tesla Model series has achieved a breakthrough, and Model 3 is about to increase its sales, further demonstrating the feasibility of ternary lithium power batteries. Model3 uses a new 21700 battery, which is longer and thicker in appearance than the 18650 battery, and its energy density has also increased by 20%. The single battery capacity can reach 3~4.8Ah, which is a significant increase of 35%. There is no doubt that the current ternary lithium power battery is already a mainstream product.

2.Solid-state lithium battery: has great technical potential and is expected to become mainstream products in the future

From the perspective of technical potential, it is relatively difficult to increase the energy density of ternary lithium power batteries, and it is more feasible in theory to increase the energy density of all-solid-state lithium batteries. First, the voltage platform of all solid-state lithium batteries has increased. Solid electrolytes generally have a wider electrochemical window than organic electrolytes, which is conducive to further improving the energy density of batteries; second, solid electrolytes can block the growth of lithium dendrites, and the range of material application systems is large. The improvement lays the foundation for a new type of lithium battery technology with higher energy density space. Third, the current energy density of all-solid-state lithium batteries is about 400Wh/Kg, and the estimated maximum potential value is 900Wh/Kg, with more than 100% room for improvement. Solid-state lithium batteries are bound to be the mainstream products in the future.

Table 5 Comparison of technical performance between ternary lithium battery and solid-state lithium battery

3.Solid-state lithium battery: high safety, which can greatly reduce the spontaneous combustion rate of vehicles

In recent years, there have been many spontaneous combustion accidents of new energy vehicles at home and abroad, and more and more attention has been paid to the use of new energy vehicles. The main reason lies in the problem of power batteries (mainly ternary lithium). The electrical safety, functional safety, chemical safety, and mechanical safety of ternary lithium batteries are still ineffective. Generally speaking, the liquid electrolyte of ternary lithium battery is flammable and explosive, and it is easy to trigger "thermal runaway" during long-term use. The growth of lithium dendrites during charging and discharging can easily pierce the diaphragm, causing short circuits in the battery and posing safety hazards. However, the all-solid-state lithium battery has extremely high safety. Its solid-state electrolyte is non-flammable, non-corrosive, non-volatile, and non-leakage. It also overcomes the phenomenon of lithium dendrites. The probability of spontaneous combustion of cars equipped with all-solid-state lithium batteries will be greatly reduce.

Based on the comparison of the above-mentioned products, technology, safety, etc., all-solid-state lithium batteries have absolute advantages in terms of safety and technical potential, but ternary lithium batteries have considerable advantages in product maturity and market penetration. On the whole, the current use of ternary lithium battery is the most wise choice for pure electric vehicles. However, once the all-solid-state lithium battery solves the problems of poor stability of metal lithium, it will explode with strong product substitution, or will subvert the power battery industry pattern.

4. Prediction of the development pattern of high-energy power batteries

As mentioned above, the country’s policy orientation has been very clear, and it strongly supports the development of new high-energy-density lithium-ion power batteries, and has been reflected in the corresponding policy details. It is mainly manifested in three aspects: one is the dual points policy issued by the Ministry of Industry and Information Technology in June 2017, when the low energy consumption Y per 100 kilometers is obtained by reducing the battery quality through high energy density, you can get 1.2 times the points; the second is the end of last year The subsidy policy emphasizes high energy density (passenger car battery energy density>120Wh/Kg), 1.1 to 1.2 times the subsidy can be obtained; third, from the perspective of the new energy vehicle promotion catalog that must be entered to obtain subsidies, passenger car three The proportion of yuan lithium battery models continues to increase, and the share of the sixth batch of models this year accounted for more than 70%, which has already promoted the development of high-energy-density batteries.

However, although domestic new energy vehicles have achieved good results in the promotion and application of new energy vehicles, pure electric passenger vehicle products for private consumers are still subject to the influence of "mileage anxiety" and have not yet achieved large-scale applications. The breakthrough in the private demand-side market and meeting requirements have further improved the energy density of power batteries. As far as the current situation is concerned, only ternary lithium power batteries and solid-state lithium power batteries may reach the 2020 goal. This will trigger a new pattern of domestic power battery technology.

The first category, leading technology, is represented by CATL. The CATL enterprise itself already has the ternary lithium battery technology precipitation, and its products will use silicon carbon materials as the negative electrode. During the "13th Five-Year Plan" period, it is expected to achieve the 350Wh/kg target; at the same time, CATL is in solid state lithium batteries (lithium-sulfur batteries, polymer batteries). ) Have achieved breakthroughs. For example, the polymer cell with a capacity of 325mAh designed and manufactured by CATL performs well in high temperature cycling. Technology leadership and advance layout can ensure that enterprises occupy the commanding heights in the application and promotion of new technologies.

The second type is technology-following type, represented by Guoxuan Hi-Tech and Lishen. Companies such as Guoxuan Hi-Tech and Lishen have a strong market foundation and are accelerating the development of ternary lithium battery technology with high battery energy density. For example, the official website of the Ministry of Science and Technology on the breakthrough of Guoxuan Hi-Tech's ternary lithium battery technology stated that it uses "high nickel cathode + silicon-based anode" as the battery material, and the energy density of the laboratory battery reaches 281Wh/kg. However, such companies rarely or basically do not involve solid-state lithium battery technology reserves. Such companies may accelerate joint venture cooperation with Samsung Japan Research Institute, Sakti3 (US), Qingtao Energy and other companies with all-solid-state lithium battery technology.

The third category, technology transformation category, pays tribute to BYD and Wanxiang. BYD, Wanxiang and other companies have limited room for the energy density of their core products, lithium iron phosphate batteries, to gradually reduce the impact of lithium iron phosphate batteries, and accelerate the transformation of the ternary lithium battery technology route. Among them, the energy density of Wanxiang's A123Systems lithium iron phosphate products has stopped at about 140Wh/kg; BYD plans to reach about 240Wh/kg in ternary lithium batteries in 2018 and 300Wh/kg in 2020. Such enterprises have strong technical accumulation and R&D support, and have a strong technological sense. They may strengthen cooperation with scientific research institutes such as the Qingdao Institute of Energy of the Chinese Academy of Sciences, the National Energy Battery Research Institute and other scientific research institutes to accelerate the research and development of all-solid-state power batteries.

All in all, the lithium iron phosphate technology route is being replaced, and the ternary lithium battery technology route has become the mainstream. The future all-solid-state lithium battery or new lithium ion battery technology route will gradually replace the ternary lithium battery.

3. Development Suggestions

In the future, the health and large-scale promotion and application of new energy vehicles depend to a large extent on the support of high-safety, high-endurance power batteries. At present, the technological progress of new energy vehicle power battery technology is driven by the dual pressure of national policies and external competition, which requires the continuous improvement of the existing ternary lithium power battery technology. At the same time, it also requires new technological breakthroughs and breakthroughs in lithium-ion batteries to achieve subversion. Sexual innovation. For power battery companies, now is the best period and the worst period. Zhidian Automobile believes that the "tough battle" of battery energy density has begun, and the power battery industry pattern will be shuffled. In the future, if companies want to enter the competitive echelon, they need to focus on two points: First, they must change their way of thinking and "be prepared for danger in times of peace", from extensive and large-scale development to a development model that emphasizes both "technology and scale", and accelerate all-solid-state lithium batteries or New lithium-ion battery technology reserves; second, we must pay attention to product safety, not only to strengthen cooperation with vehicle companies, but also to avoid the "Takata airbag" incident in the power battery industry.