A few days ago, big news in the domestic power battery industry broke out frequently. First, SAIC entered the power battery sector, and it married with Ningde Times, the second largest power battery company in China and the third largest power battery company in the world, to establish a power battery system company; then there was news that BYD would spin off The power battery department will open its doors or supply to all car companies. There are reports that this move may change the global market.
A few days ago, big news in the domestic power battery industry broke out frequently. First, SAIC entered the power battery sector, and it married with Ningde Times, the second largest power battery company in China and the third largest power battery company in the world, to establish a power battery system company; then there was news that BYD would spin off The power battery department will open its doors or supply to all car companies. There are reports that this move may change the global market. Moreover, the domestic electric vehicle market has ranked first in the world in terms of production and sales for two consecutive years, with a cumulative promotion of more than 1 million vehicles, accounting for more than 50% of the global market. China surpasses the United States to take the top spot in the electric vehicle market. It can be said that the electric vehicle industry has unlimited prospects and rapid development. The key lies in the improvement of power battery technology.
The development of electric vehicles requires better batteries. The specific energy, life, safety and price of power batteries are essential to the development of pure electric vehicles. Among them, lithium-ion batteries, which have the advantages of high specific energy and long life, are currently the most practical and valuable electric vehicle batteries, and are widely used in hybrid vehicles, pure electric vehicles and fuel cell vehicles. The current technical level of commercial power batteries and the expected achievable goals in the next 10 years are shown in Figure 1. In actual product production, these indicators are often contradictory, and battery-related performance needs to be weighed and considered. The improvement of battery performance needs to take into account the performance of electrode materials, electrolytes, and separators. At the same time, the follow-up of assembly technology, battery system grouping, and management technology is also crucial. This article aims to summarize the current development achievements of power batteries with lithium-ion batteries as the core from the aspects of battery material technology, single battery design and manufacturing technology, and battery system technology, while looking forward to the future!
1. Positive and negative materials
Lithium battery cathode and anode material systems are very rich (Figure 2). At present, research on cathode materials such as lithium cobaltate, lithium manganate, lithium iron phosphate, and lithium nickel cobalt manganese has become mature. The specific capacity of lithium cobalt oxide material is 200-210mA·h/g, and its true density and pole piece compaction density are both the highest among existing cathode materials. The charging voltage of the commercial lithium cobalt oxide/graphite system can be increased by 4.40V. It can already meet the demand for high-volume energy-density soft pack batteries for smart phones and tablet computers. Lithium manganate has low raw material cost, simple production process, high thermal stability, good overcharge resistance, high discharge voltage platform, and high safety. It is suitable as a low-cost battery for light electric vehicles, but it has a relatively low theoretical capacity, and the dissolution of manganese may affect the battery life in a high-temperature environment during the cycle. Domestic lithium manganate materials mainly meet the needs of the mobile power supply, power tools and electric bicycle markets, and have a trend of low-end development. NCM ternary layered cathode materials are mainly used in power batteries. Except for LiNi1/3Co1/3Mn1/3O2, which accounts for 1/3 of each of nickel, cobalt, and manganese, which are more mature in power batteries, the higher capacity LiNi0.5Co0 .2Mn0.3O2 has also entered batch applications, and is generally mixed with lithium manganate for electric vehicle batteries. The energy density of aluminum-doped lithium nickel cobalt oxygen (NCA) can be close to that of high-voltage lithium cobalt oxide batteries. In recent years, electric vehicle manufacturer Tesla has used this computer battery to drive electric vehicles. This material can also be combined with lithium manganate. The hybrid is used to manufacture automotive power batteries. The domestic NCA precursor has formed a stable production capacity. A few companies have completed the development of NCA cathode materials and are in the process of product promotion. Lithium iron phosphate batteries have high safety and long life. At present, nano-sized power materials and high-density lithium iron manganese phosphate materials are developing rapidly. The performance of high-energy and high-power materials tends to be stable, and the cost is further reduced. Gradually satisfying the domestic market demand and the need for the promotion of new energy vehicles in China at this stage, high-voltage spinel lithium nickel manganese oxide and high-voltage high specific capacity lithium-rich manganese-based cathode materials are still under development.
2. Anode material
The negative electrode materials that can be used for power batteries include graphite, hard/soft carbon and alloy materials. Graphite is currently a widely used negative electrode material, and its reversible capacity has reached 360mA·h/g. Amorphous hard carbon or soft carbon can meet the requirements of higher rate and lower temperature applications of batteries, and they are beginning to be applied, but they are mainly mixed with graphite. Lithium titanate anode material has the best rate performance and cycle performance, and is suitable for high-current fast charging batteries, but the produced batteries have lower specific energy and higher cost. Nano-silicon was proposed in the 1990s to be used for high-capacity anodes. Improving the capacity of carbon anode materials with a small amount of nano-silicon doping is a hot spot in current research and development. Anode materials with a small amount of nano-silicon or silicon oxide have begun to enter small batches. In the application stage, the reversible capacity reaches 450mA·h/g. However, due to the volume expansion caused by lithium intercalation in silicon, the problem of reduced cycle life in actual use needs to be further resolved.