With the rapid rise of sales of new energy vehicles, power batteries have also developed rapidly. Relevant statistics show that the total amount of lithium batteries in China reached 28gwh in 2016, a number of super large battery manufacturers have emerged, and battery technology has made great progress.

On the whole, the development direction of domestic battery technology tends to be clear, which lays a foundation for subsequent development. At the same time, indicators such as battery fast charging, service life and energy density need to be further optimized.

The technical route tends to be clear

How to choose ternary, lithium iron phosphate and lithium titanate material systems? How to choose between cylindrical, square and soft package structure? There were many disputes before.

However, with the rapid development of the new energy vehicle market, the development and application direction of ternary, lithium iron, lithium manganate and lithium titanate batteries in the industry has gradually become the same. The mainstream status of ternary batteries and lithium iron phosphate batteries has become more and more consolidated. Ternary batteries with high energy density will dominate the new energy passenger vehicle market, and lithium iron batteries with good thermal stability are the main force in the passenger car market.
 

With the improvement of the reliability of ternary batteries and the cancellation of restrictions on the bus market, the 2:7 ratio of ternary batteries to lithium iron phosphate batteries will be broken. Among them, the proportion of ternary batteries will be further expanded, while lithium titanate batteries will still occupy a certain proportion in the field of fast charging buses and taxis due to the characteristics of long theoretical life and short fast charging time. However, due to the "bias" in energy density and price, it also determines its supporting role in the field of power batteries. I personally believe that energy storage will be an important field for lithium titanate batteries to give full play to their strengths.

Silicon carbide, lithium sulfur, lithium air and graphene, and even solid-state polymer batteries still belong to laboratory technology, which is still a certain distance from industrialization. For example, graphene, which has been under constant discussion, is best used as an additive to rapidly conduct heat, while it remains to be broken through as the main component of the negative or positive material of power batteries.

Lithium batteries with cylindrical, square and soft package structure rely on their own technical characteristics to find the most suitable technical fields for their application. Cylindrical batteries have price advantages and are suitable for the layout of special-shaped bags, and occupy the mainstream in the field of private cars and logistics vehicles; Square and soft pack batteries can overcome the disadvantages of large heat dissipation of cylindrical batteries, and are suitable for taxis and online taxi Hailing vehicles with strict fast charging requirements.

In the battery game between square and soft package structure, due to the route selection of enterprises such as catl, BYD and GuoXuan high tech in China, the battery advantage of square structure is obvious. However, looking at the world pattern, with the market demand for batteries with energy density of 300wh / kg or even 500wh / kg, the advantage of soft package structure in energy density will be well reflected, and the high safety of soft package will gradually increase.

Battery performance needs to be improved

The battery performance follows the "barrel law", and the battery pack is calculated based on the single or module with the worst performance, which requires the improvement of single cell manufacturing, group process and battery pack integration technology.

The performance of existing batteries can meet the needs of specific models. For example, in terms of thermal management, the speed of passenger cars is low, the space around the battery pack is large, and the air fluidity is good, which can be met by mainstream natural air cooling. In terms of battery life, the warranty of 8 years or 120000 kilometers basically meets the needs of private cars.

The market share of class a new energy vehicles is an important indicator that truly reflects the technological development and user acceptance. At present, taxis and online car Hailing are the main markets for class a pure electric vehicles, and the actual performance of batteries can not meet the vehicle demand in this field.

There are special requirements for the fast charging speed of taxis, online car hailing and other models, especially in the case of "hot car" and "cold car". It takes 30 ~ 40 minutes for the battery to reach 10% ~ 80% at room temperature. However, when the vehicle runs through a cycle in summer, the temperature of the naturally air-cooled battery pack is close to 45 degrees, and some batteries even exceed 50 degrees, the ternary battery starts to limit the current, the charging speed slows down, and the time is extended by more than three times, which can not meet the needs of online car hailing and taxis.

Similarly, below zero, the charging current is zero or only one tenth of that at room temperature. In this regard, the existing method is to add PTC or heating resistance wire, but this method will generally lead to uneven cooling and heating, and the difference between the maximum and minimum temperatures is large, which will affect the service life of the battery pack.

Since 2017, the application trend of liquid cooling or direct cooling and heat management system has been obvious, some models have begun to be used in batches, and other vehicle enterprises are also accelerating the development to solve the problem of fast charging speed.

In addition to the fast charging index, battery life is also one of the biggest problems to test the battery. In general, the annual mileage of taxis and online car hailing in large and medium-sized cities is 70000 ~ 80000 kilometers, while in first tier cities such as Beijing and Shanghai, the annual mileage is more than 120000 kilometers. The warranty requirements for electric vehicles in the taxi market are 6 years or 400000 kilometers, some even 8 years or 600000 kilometers, but the existing battery standard of 8 years or 120000 kilometers can not meet the requirements at all.

In recent years, with the improvement of process quality, the cycle life of the battery has increased from 1000 times to 2000 times, or even to 3000 times, which is no less than 80% of the initial discharge capacity. For example, some domestic battery manufacturers promise BMW that the initial discharge capacity of the battery cell will reach more than 80% per 10000 times. Although it is shallow charge and shallow discharge, it can also be seen that the battery life will increase rapidly.

Low energy density of the whole package

The energy density of 180wh / kg is the higher technology of ternary monomer battery in China. The energy density of lithium iron phosphate battery is about 80% of ternary battery, and lithium titanate is less than half of ternary battery. Compared with foreign countries, there is still a large gap between the energy density of domestic batteries. For example, Tesla has achieved 236wh / kg battery energy density three or four years ago.

The battery energy density not only affects the driving range of the vehicle, but also affects the lightweight process of the vehicle. The body weight of A-class car is about 450kg. If you want to achieve 150kg weight reduction, you need to carry out revolutionary transformation of the four processes, which is costly and long cycle.

For example, if the energy density of a 60 kwh battery pack is increased by 20%, that is, from 180wh / kg to 220wh / kg, the effect is comparable to the revolutionary transformation of the four processes.

Therefore, the roadmap of energy saving and new energy vehicle technology proposes that by 2020, the energy density of domestic pure electric vehicle power battery will reach 350wh / kg, which is of great significance, but it also faces many technical and technological challenges.

How to meet the production of battery packs? According to the requirements of foreign enterprises for product standards, the introduction of international first-class companies for joint venture or sole proprietorship is one of the best methods. The "wolf" may lead to intensified competition in the short term, but it will generally accelerate the survival of the fittest of domestic power battery manufacturers, promote the rapid development of domestic battery technology, and even improve the whole ecological chain technologies such as lithium extraction from Salt Lake, lithium carbonate preparation, positive electrode, negative electrode and diaphragm.