Discussing the impact of LR41 battery on fast charging of new energy vehicles

When using electric vehicles, consumers are most worried about the charging time and cruising range. Under the current technical level, it is difficult to have both charging time and cruising range. Therefore, power LR41 battery have developed two routes. One is the energy-specific faction that focuses on cruising range, mainly by continuously improving the specific energy of lithium-ion LR41 battery, thereby increasing the cruising range of electric vehicles; the second is the fast charging faction that focuses on reducing charging time, mainly by improving the fast charging performance of lithium-ion LR41 battery and shortening the charging time of electric vehicles. With the advancement of technology and in-depth research on lithium battery materials, the problems that fast charging technology has encountered may also be solved one by one.

1. How to understand fast charging?

To understand fast charging, a professional term cannot be avoided-the charge and discharge rate C, which can be simply understood as the rate of charge and discharge. The charge and discharge rate of lithium-ion LR41 battery determines how fast we can store a certain amount of energy in the battery, or how fast we can release the energy in the battery.

According to the 2018 new energy vehicle subsidy policy, a charging rate of less than 3C is classified as a non-fast charging pure electric bus, and a charging rate of more than (including) 3C is classified as a fast charging pure electric bus. However, the fast charging subsidy classification is only for new energy buses, and there is no standard for passenger cars and logistics vehicles.

According to the definition of the industry and CATL, electric vehicle fast charging refers to a charging method with a charging current greater than 1.6C, that is, a technology that charges from 0% to 80% in less than 30 minutes. Based on the opinions of many parties, the author proposes that a charging rate of less than 1.6C is slow charging, 1.6C-3C is small fast charging, and 3C or more is fast charging. Most electric passenger cars can achieve "small fast charging", and the charging rate of fast charging buses is mostly concentrated in 3C-5C.

If we compare the lithium-ion battery to a rocking chair, the two ends of the rocking chair are the two poles of the battery, and the lithium ions are like excellent athletes, running back and forth at the two ends of the rocking chair. When charging, lithium ions are generated on the positive electrode of the battery, and the generated lithium ions move to the negative electrode through the electrolyte. The carbon as the negative electrode has a layered structure, and it has many micropores for the lithium ions that reach the negative electrode to be embedded. The more lithium ions embedded, the higher the charging capacity.

During fast charging, lithium ions need to be accelerated and instantly embedded into the negative electrode. This poses a great challenge to the ability of the negative electrode to quickly receive lithium ions. LR41 battery of ordinary chemical systems will have byproducts at the negative electrode during fast charging, affecting the cycle and stability of the battery cell. Energy density and power density can be said to be two directions that lose one thing while taking care of the other in the same battery.

Whether it is national policy orientation or corporate technology layout, high energy density is generally pursued. When the energy density of the power battery is high enough and the power load of a car is large enough, the so-called "mileage anxiety" can be avoided, and the demand for fast charging will be reduced. However, if the power is large, it will be difficult to be accepted by the market if the cost is not reduced. Therefore, if the battery cost can be controlled, the user anxiety can be greatly alleviated with convenient charging capacity + applicable cruising range, so that fast charging has value.

2. Fast charging application prospects of LR41 battery with different technical routes

The speed of charging is closely related to the overall technical and design requirements of power LR41 battery, charging piles, electric vehicles, power grids, etc., among which the biggest influencing factor is still the battery. Let's discuss the application trends of different types of power LR41 battery in the direction of fast charging technology. Almost all kinds of positive electrode materials can be used to make fast-charging LR41 battery, but their applicability and advantages and disadvantages vary.

1. Ternary fast-charging LR41 battery are more suitable for electric passenger cars

Ternary LR41 battery are more valued because of their higher energy density. The material itself has excellent conductivity, but the reaction activity is too high, which poses a greater challenge to fast charging safety.

Representative companies of ternary battery fast charging systems include CATL and BAK. CATL has developed "superconducting electronic network" and "fast ion ring" technologies, which can achieve SOC charging from 5% to 85% within 15 minutes, energy density of 190Wh/kg, and cycle life of more than 2,500 times. The main application area is passenger cars, and it is expected to have mass production capabilities in 2018.

The 3.0 high-energy core newly launched by BYD in May this year has an energy density of nearly 250Wh/kg by introducing silicon-based negative electrode materials, high-nickel positive electrode materials, and specially developed electrolytes, which can achieve an ultra-long range of 500 kilometers. Through the design of charging strategies, the charging time is effectively shortened and the charging efficiency is improved. In extreme emergency mode, it can travel 60 kilometers after charging for 10 minutes.

According to the usage habits of fuel vehicles, to achieve a full charge within 10-20 minutes, the charging rate needs to be at least 3-6C. At present, most of the pure electric passenger cars on the market are fully charged to 80% in half an hour to one hour, which has improved a lot compared to the previous two or three hours of charging time. In the future, it is expected to be further compressed to within 20 minutes.

2. Lithium iron phosphate fast charging is available for both passenger and commercial vehicles

Lithium iron phosphate does not have an inherent advantage in the field of fast charging. From the material point of view, the intrinsic conductivity of lithium iron phosphate materials is relatively low, only one percent of that of ternary materials. The conductivity of lithium iron phosphate materials needs to be optimized to meet the needs of fast charging. However, the material cost of lithium iron phosphate is relatively low. Combined with mature technical background and stable product performance, it has a relatively broad application prospect. Representative companies include CATL, Watma, etc.

Limited by the extreme value limit of theoretical energy density, lithium iron phosphate has little room for development in terms of energy density in the future. However, for commercial vehicles such as buses, logistics vehicles, and special vehicles that have already adopted the lithium iron phosphate system, it is not necessary to improve the energy density, and fast charging is increasingly showing its importance.

3. Lithium manganese oxide LR41 battery are suitable for plug-in hybrid buses

Lithium manganese oxide LR41 battery have the characteristics of power performance, discharge rate performance, good low temperature performance, and high voltage frequency. In the situation of crazy rise in upstream raw materials of ternary materials, the cost advantage of lithium manganese oxide is gradually emerging. However, there is still a need to improve energy density and high temperature performance. In recent years, the proportion of lithium manganese oxide fast-charging LR41 battery in the field of plug-in hybrid buses has increased significantly, and representative companies are CITIC Guoan Mengguli, Yipeng New Energy, and Microvast Power.

However, the cycle performance of lithium manganese oxide LR41 battery is poor under high temperature conditions. The high temperature performance of lithium manganese oxide LR41 battery can be improved by positive electrode doping, but the modified lithium manganese oxide material is no longer the "original lithium manganese oxide". The industry often uses "multi-composite materials", with the positive electrode using a mixed system of ternary materials and lithium manganese oxide, and the negative electrode using porous composite carbon to further improve the performance of fast charging, but safety still needs to be focused on and continuously improved.

4. Lithium titanate fast charging battery is suitable for pure electric buses

Lithium titanate power LR41 battery are named after the negative electrode material, and the positive electrode uses ternary materials. Zhuhai Yinlong, Weihong Power, and Tianjin Jiewei are typical companies. In terms of performance, lithium titanate LR41 battery have excellent low-temperature performance, good safety and cycle performance, and their rate performance as fast-charging LR41 battery has also been recognized by the industry. However, there are two prominent problems with lithium titanate at present: First, the energy density is relatively low. Under the pressure of policies and markets that require continuous improvement in energy density, the current market share of lithium titanate is relatively low in the entire power battery market. Secondly, due to the high cost of small metal materials such as titanium, nickel and cobalt, the cost of lithium titanate LR41 battery is significantly higher than other systems.

Lithium titanate LR41 battery are significantly better than other fast-charging LR41 battery in terms of cycle life, which is determined by the characteristics of the material itself, namely the "zero strain" characteristic. However, its disadvantages are obvious, with low energy density, which is only about half of the energy density of the ternary system. In addition, the price is relatively high. At present, it is mostly used in fast-charging buses. In the future, it is urgent to seek higher voltage positive electrode materials and matching electrolytes to solve this defect.

5. New direction of fast charging-titanium niobium oxide negative electrode material

Titanium niobium oxide is developed based on lithium titanate. The main advantage is that compared with the theoretical capacity of lithium titanate of 175mAh/g, the theoretical capacity of titanium niobium oxide is about 280mAh/g.

In October 2017, Toshiba officially announced that it had successfully developed a new generation of automotive lithium-ion LR41 battery, which is expected to be commercialized in 2019. The battery uses titanium niobium oxide materials, which is a disruptive progress compared to the current ternary and lithium iron phosphate technologies. The new battery has the advantages of high energy density and fast charging efficiency. It only takes 6 minutes to charge to 90% of the power and can travel 320 kilometers. At present, it takes an average of 30 minutes for lithium LR41 battery to charge to 80% of the power.

In addition, the concept of "graphene battery" has been quite popular, but there are also disputes in the industry. In lithium LR41 battery, graphene is mainly used as negative electrode active materials and conductive additives. In terms of fast charging capability alone, using graphene as a conductive agent or coating lithium iron phosphate/ternary lithium materials with graphene can achieve better fast charging effects. However, from the perspective of comprehensive cost, process difficulty and other indicators, it is still very challenging.

3. Market prospects of fast charging products

High energy density, fast charging and low price are the ideal power battery products that users are most looking forward to. However, "you can't have your cake and eat it too". Under the existing lithium-ion battery system, the five most important indicators of power LR41 battery, such as rate performance, energy density, life, safety and price, are fixed in relatively stable special graphs. If any one indicator is improved, other indicators will be relatively lost.

At present, fast-charging power LR41 battery are mainly used in new energy buses because they are highly selective for cities and target units, that is, cities or units with relatively financial support tend to prefer fast-charging battery buses. However, from the perspective of market development potential, the growth rate and market size of passenger cars and special logistics vehicles will be higher than that of buses in the future, so the consumption structure of fast-charging power LR41 battery will shift to these two types of vehicles in the future.

According to Battery China data, my country's fast-charging bus production in 2017 was 6,486 units, and the battery installed capacity reached 597.52MWh, accounting for 6% of the total new energy buses. Among them, the highest charging rate of fast-charging bus products is 6.42C. The production of models with a rate of 3C-5C is 4,771 units, and the battery installed capacity is 480.68MWh; the production of models with a rate of 5C-10C is 1,715 units, and the battery installed capacity is 116.84MWh. At present, the fast-charging rates of fast-charging buses are mainly concentrated between 3C-5C. From the perspective of battery types, the battery materials for fast-charging buses in 2017 were mainly lithium titanate, with an installed capacity of 571.54Mwh, accounting for 95.65%.

According to the shipments of four types of power LR41 battery in 2017, 1.54GWh of lithium manganate was partially used in plug-in hybrid vehicles, partially met the requirements of small fast charging, and 16GWh of ternary battery vehicles partially met the requirements of small fast charging. Overall, ternary fast-charging LR41 battery are suitable for passenger cars, fast-charging LR41 battery such as lithium iron phosphate and lithium titanate are suitable for buses, lithium manganate fast-charging LR41 battery are suitable for plug-in hybrid vehicles, and titanium niobium oxide may be a new direction for fast charging.

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