Analysis on the problem of fast charging of vehicle power lithium battery -Lithium - Ion Battery Equipment
When it comes to new energy vehicles, it is natural to talk about power lithium-ion batteries, and batteries are both familiar and unfamiliar to most of us. What is familiar is that batteries exist in all aspects of use around us, but what is unfamiliar is its ins and outs and temperament. The ternary lithium ion, which is widely used in new energy vehicles, is a constantly updated battery system, involving many research fields in physics and chemistry. This makes people lack in-depth and rational understanding of lithium-ion batteries, and this series of articles will try to make a simple analysis of the issues related to vehicle-mounted power lithium-ion batteries, hoping to be helpful to friends.
The slow charging speed, especially compared to the experience of filling up the fuel tank in a few minutes for fuel vehicles, is too large, which is an important pain point for current new energy vehicles. In response to this problem, fast charging is regarded as an important indicator of vehicles in many publicity. Fast charging can really improve the convenience of electric vehicles, but we should also realize that fast charging also brings a series of problems.(Lithium - Ion Battery Equipment)
1. The problem of fast charging
When it comes to charging, our requirements are actually simple: fast, efficient, and safe. In layman's terms, it means charging as fast as possible without danger or harming my battery, and don't waste it during charging. The participants included in fast charging include batteries, chargers and supporting facilities, so the discussion of fast charging is naturally inseparable from these three participants.
1. Fast charging rate
First of all, let's clarify what fast charging is. The meaning of fast charging in the industry is not based on the detailed charging power, but based on an indicator called charging rate, the unit is C. Generally speaking, the charging rate means that a battery takes several times longer than one hour to charge, 1C for 1 hour, 0.5C for 2 hours, and 2C for half an hour. According to earlier international recommended standards, a rate exceeding 0.1C can be called fast charging. In the current electric vehicles, the national standard for commercial vehicles is 3C, while for passenger vehicles it is almost 1.6C to be called fast charging. However, the current fast charging rate of passenger cars is around 1C-1.2C.
Therefore, compared with a car with a charging capacity of 60kWh and a charging power of 60kW, compared with a car with a charging capacity of 40kWh and a charging power of 50kW, the fast charging capability of a car with a charging power of 50kW is actually stronger.
2. Fast charging participants
Batteries, chargers and supporting facilities, chargers are relatively easy in terms of implementation difficulty, but batteries and supporting facilities are facing a headache.
Charging pile
At present, there are news of high-power fast charging piles at home and abroad, but its own critical issues are actually how to commercialize and how to balance costs. And more questions are what kind of battery can withstand such a large charging rate (currently the maximum charging capacity of a passenger car is only 100kWh, and 500kW charging will bring a 5C charging rate), and such a large breakthrough How to do a good job of power grid matching for power generation and consumption.
Battery
Let me talk about lithium-ion batteries first, which is a relatively new type of secondary battery (commonly known as rechargeable batteries, which are used repeatedly; corresponding to disposable dry batteries, which are primary batteries). The characteristics of charging and discharging are widely used in the current field of new energy vehicles.
The fast charging capability we want is based on the physical and chemical structural characteristics of lithium-ion batteries, and has its inherent scientific laws, and it is impossible to "release satellites" out of thin air. Lithium-ion battery fast charging requires efforts in all aspects of the battery as a whole, including positive electrodes, negative electrodes, electrolytes, diaphragms, and structural design. Among them, the positive electrode material and structural design are currently the smallest part of the bottleneck, while the negative electrode, diaphragm, and electrolyte all have serious contradictions in terms of fast charging, safety, and life.
As for the negative electrode, fast charging and high current bring about greater pressure on the negative electrode to quickly accept lithium, which in turn increases the tendency to form lithium dendrites. Therefore, the negative electrode must not only meet the kinetic requirements of lithium diffusion during fast charging, but also deal with the safety issues caused by the increased tendency of lithium dendrite formation. Therefore, the key technical difficulty of fast charging cores is actually the embedding of lithium ions in the negative electrode. Due to cost constraints, graphite is still the main material. Although the comprehensive production performance and energy density of graphite are relatively excellent, its surface is relatively sensitive to the electrolyte, which also has a negative impact on the battery safety during fast charging, especially after the diaphragm is broken due to dendrite growth.
The electrolyte has a great influence on the performance of fast-charging lithium-ion batteries. To ensure the stability and safety of the battery under fast charging and high current, the electrolyte must be unanalyzable, have high conductivity, be inert to the positive and negative electrode materials, and cannot react or dissolve. If these requirements are to be met, the key is to use additives and functional electrolytes. In detail, the ternary lithium-ion battery must be protected by adding various high-temperature resistant, flame-retardant, and overcharge-proof additives to improve its safety to a certain extent.
The diaphragm is the key to isolating the positive and negative electrodes and preventing internal short circuits, while fast charging puts considerable pressure on the safety and life of the diaphragm. Especially in recent years, some domestic companies have greatly reduced the thickness of the diaphragm due to the excessive pursuit of the energy density of the monomer, which has caused certain hidden dangers in the ability of the diaphragm to respond to dendrite puncture.
It should be noted that there is a situation where the accumulation and puncture of dendrites is on the verge of critical limit and even many micro-short circuits have appeared, but the heat generated is slowly increasing the temperature of the battery, but it is not high enough to cause the material to burn, and the gas generated is not high enough. Enough to break the battery case. At this time, after a period of time, the battery will explode. This is one of the reasons why it is difficult for us to accurately predict battery fires.
There is another problem related to the actual interests of users in battery charging, that is, fast charging will cause a large degree of "floating power" problem, which is what we often say that the battery after fast charging is not durable.
Therefore, before the battery technology has made significant progress, it is impossible for the battery to make a leap forward in fast charging performance under the premise of ensuring its own comprehensive performance balance.
supporting facilities
The most important supporting requirement for fast charging is grid adaptation. Regardless of the huge power consumption or the sudden power consumption, it has put a great pressure on the existing power grid, and it is well known that the adaptability of the power grid is very limited, and it is impossible to deal with the increasingly rapid development and base without limit. The fast charging demand of new energy vehicles is increasing.
Therefore, it is impossible for fast charging to become the mainstream charging form. "Slow charging as the mainstay and fast charging as an emergency" will be an important ecology of new energy vehicle charging for a long period of time.
2 Future development of charging
2. Future development of charging
In fact, the root of our pursuit of fast charging is the pursuit of the convenience of using battery cars, and the way to improve convenience is not just fast charging.
Future charging is likely to be in the form of wired slow charging, wired fast charging, wireless slow charging, wireless fast charging, and quick battery replacement, among which wireless charging will be deeply integrated with autonomous driving technology.
With the sharp increase in the number of electric vehicles, one of the added values of new energy vehicles will be greatly developed in the future, that is, through V2G (interconnection and interaction between vehicles and power grids), the peak and frequency regulation of the power grid will be realized. social benefits. As far as the car owner is concerned, his private car will be used as a small energy storage station, which will not only greatly reduce the cost of using the car, but may even have certain additional benefits.
Conclusion:
History has long proved that the destructiveness and tolerance of a blind follower group are shocking, but a mature and rational auto market and user groups are beneficial to the long-term healthy development of OEMs. At this period of great change and transformation in the auto industry, it is also a good time to guide and cultivate a healthy auto market in my country. Moderate and accurate information dissemination is the correct approach. The same is true for fast charging.
The slow charging speed, especially compared to the experience of filling up the fuel tank in a few minutes for fuel vehicles, is too large, which is an important pain point for current new energy vehicles. In response to this problem, fast charging is regarded as an important indicator of vehicles in many publicity. Fast charging can really improve the convenience of electric vehicles, but we should also realize that fast charging also brings a series of problems.(Lithium - Ion Battery Equipment)
1. The problem of fast charging
When it comes to charging, our requirements are actually simple: fast, efficient, and safe. In layman's terms, it means charging as fast as possible without danger or harming my battery, and don't waste it during charging. The participants included in fast charging include batteries, chargers and supporting facilities, so the discussion of fast charging is naturally inseparable from these three participants.
1. Fast charging rate
First of all, let's clarify what fast charging is. The meaning of fast charging in the industry is not based on the detailed charging power, but based on an indicator called charging rate, the unit is C. Generally speaking, the charging rate means that a battery takes several times longer than one hour to charge, 1C for 1 hour, 0.5C for 2 hours, and 2C for half an hour. According to earlier international recommended standards, a rate exceeding 0.1C can be called fast charging. In the current electric vehicles, the national standard for commercial vehicles is 3C, while for passenger vehicles it is almost 1.6C to be called fast charging. However, the current fast charging rate of passenger cars is around 1C-1.2C.
Therefore, compared with a car with a charging capacity of 60kWh and a charging power of 60kW, compared with a car with a charging capacity of 40kWh and a charging power of 50kW, the fast charging capability of a car with a charging power of 50kW is actually stronger.
2. Fast charging participants
Batteries, chargers and supporting facilities, chargers are relatively easy in terms of implementation difficulty, but batteries and supporting facilities are facing a headache.
Charging pile
At present, there are news of high-power fast charging piles at home and abroad, but its own critical issues are actually how to commercialize and how to balance costs. And more questions are what kind of battery can withstand such a large charging rate (currently the maximum charging capacity of a passenger car is only 100kWh, and 500kW charging will bring a 5C charging rate), and such a large breakthrough How to do a good job of power grid matching for power generation and consumption.
Battery
Let me talk about lithium-ion batteries first, which is a relatively new type of secondary battery (commonly known as rechargeable batteries, which are used repeatedly; corresponding to disposable dry batteries, which are primary batteries). The characteristics of charging and discharging are widely used in the current field of new energy vehicles.
The fast charging capability we want is based on the physical and chemical structural characteristics of lithium-ion batteries, and has its inherent scientific laws, and it is impossible to "release satellites" out of thin air. Lithium-ion battery fast charging requires efforts in all aspects of the battery as a whole, including positive electrodes, negative electrodes, electrolytes, diaphragms, and structural design. Among them, the positive electrode material and structural design are currently the smallest part of the bottleneck, while the negative electrode, diaphragm, and electrolyte all have serious contradictions in terms of fast charging, safety, and life.
As for the negative electrode, fast charging and high current bring about greater pressure on the negative electrode to quickly accept lithium, which in turn increases the tendency to form lithium dendrites. Therefore, the negative electrode must not only meet the kinetic requirements of lithium diffusion during fast charging, but also deal with the safety issues caused by the increased tendency of lithium dendrite formation. Therefore, the key technical difficulty of fast charging cores is actually the embedding of lithium ions in the negative electrode. Due to cost constraints, graphite is still the main material. Although the comprehensive production performance and energy density of graphite are relatively excellent, its surface is relatively sensitive to the electrolyte, which also has a negative impact on the battery safety during fast charging, especially after the diaphragm is broken due to dendrite growth.
The electrolyte has a great influence on the performance of fast-charging lithium-ion batteries. To ensure the stability and safety of the battery under fast charging and high current, the electrolyte must be unanalyzable, have high conductivity, be inert to the positive and negative electrode materials, and cannot react or dissolve. If these requirements are to be met, the key is to use additives and functional electrolytes. In detail, the ternary lithium-ion battery must be protected by adding various high-temperature resistant, flame-retardant, and overcharge-proof additives to improve its safety to a certain extent.
The diaphragm is the key to isolating the positive and negative electrodes and preventing internal short circuits, while fast charging puts considerable pressure on the safety and life of the diaphragm. Especially in recent years, some domestic companies have greatly reduced the thickness of the diaphragm due to the excessive pursuit of the energy density of the monomer, which has caused certain hidden dangers in the ability of the diaphragm to respond to dendrite puncture.
It should be noted that there is a situation where the accumulation and puncture of dendrites is on the verge of critical limit and even many micro-short circuits have appeared, but the heat generated is slowly increasing the temperature of the battery, but it is not high enough to cause the material to burn, and the gas generated is not high enough. Enough to break the battery case. At this time, after a period of time, the battery will explode. This is one of the reasons why it is difficult for us to accurately predict battery fires.
There is another problem related to the actual interests of users in battery charging, that is, fast charging will cause a large degree of "floating power" problem, which is what we often say that the battery after fast charging is not durable.
Therefore, before the battery technology has made significant progress, it is impossible for the battery to make a leap forward in fast charging performance under the premise of ensuring its own comprehensive performance balance.
supporting facilities
The most important supporting requirement for fast charging is grid adaptation. Regardless of the huge power consumption or the sudden power consumption, it has put a great pressure on the existing power grid, and it is well known that the adaptability of the power grid is very limited, and it is impossible to deal with the increasingly rapid development and base without limit. The fast charging demand of new energy vehicles is increasing.
Therefore, it is impossible for fast charging to become the mainstream charging form. "Slow charging as the mainstay and fast charging as an emergency" will be an important ecology of new energy vehicle charging for a long period of time.
2 Future development of charging
2. Future development of charging
In fact, the root of our pursuit of fast charging is the pursuit of the convenience of using battery cars, and the way to improve convenience is not just fast charging.
Future charging is likely to be in the form of wired slow charging, wired fast charging, wireless slow charging, wireless fast charging, and quick battery replacement, among which wireless charging will be deeply integrated with autonomous driving technology.
With the sharp increase in the number of electric vehicles, one of the added values of new energy vehicles will be greatly developed in the future, that is, through V2G (interconnection and interaction between vehicles and power grids), the peak and frequency regulation of the power grid will be realized. social benefits. As far as the car owner is concerned, his private car will be used as a small energy storage station, which will not only greatly reduce the cost of using the car, but may even have certain additional benefits.
Conclusion:
History has long proved that the destructiveness and tolerance of a blind follower group are shocking, but a mature and rational auto market and user groups are beneficial to the long-term healthy development of OEMs. At this period of great change and transformation in the auto industry, it is also a good time to guide and cultivate a healthy auto market in my country. Moderate and accurate information dissemination is the correct approach. The same is true for fast charging.
