The superiority of lithium iron phosphate batteries.
1、 Security
Firstly, safety is an essential prerequisite for automobiles. Unlike smartphones and computers, cars may encounter numerous unpredictable factors during high-speed driving, such as battery compression and impact caused by car accidents. And any unfavorable factor could potentially lead to car accidents and fatalities. We can see that some elderly scooters use low-quality lead-acid batteries without any safety guarantee, and there are numerous cases of battery self ignition and impact combustion. For example, Tesla's continuous fire incidents in the past year, although benefiting from Tesla's safety design, did not result in any casualties. But at the same time, it should be noted that these incidents were all very minor collision accidents, and the collisions themselves did not harm the car or people, but the battery caught fire. So what if it were a more serious accident?
2、 Temperature adaptability
The impact of extreme cold on batteries is mainly manifested in low charging and discharging rates and reduced capacitance; The impact of extreme heat on batteries is mainly manifested in reduced lifespan, high temperature safety, and decreased charging and discharging capabilities.
The impact of extreme cold on batteries is relatively mild, as most lithium batteries can be used below minus 20 degrees Celsius, and heat is generated during the discharge process. However, an increase in energy consumption and a decrease in battery capacity are inevitable.
The impact of extreme cold on pure electric vehicles is different from that on dual-mode hybrid vehicles. Due to the lack of other power sources, pure electric vehicles must rely on battery discharge and heating to reach the appropriate temperature in extremely cold conditions, which will have a significant impact on energy consumption and range. Tesla's energy consumption and range during winter are significantly different from usual.
The impact on dual-mode hybrid power is relatively weak. Because hybrid vehicles have an engine as a backup to provide energy. For example, in November last year, BYD held a "Qin" promotion event in Baotou. At that time, the nighttime temperature was between minus 15 and 20 degrees Celsius. When starting the vehicle in the extremely cold morning, the system would automatically switch to HEV mode, and the engine would drive the air conditioning to quickly increase the temperature inside the car. When the temperature increased, it would switch back to EV mode.
Extreme heat has a significant impact on both pure electric and hybrid systems, for example, the high power discharge temperature of the battery itself will increase. Taking ordinary lithium-ion batteries as an example, with a discharge of 20C, the temperature of the battery can be raised to nearly 50 degrees. Such high temperatures not only affect the lifespan of the battery, but more importantly, pose a safety hazard. For example, Tesla's ternary battery releases oxygen in high temperature environments, which is a flammable substance. Tesla reduces temperature through a circulating cooling system and isolates the battery with a hard shell to prevent oxygen from escaping. But it is still inevitable to catch fire when encountering an impact.
3、 High rate discharge life
Ordinary cars have a lifespan of several decades, while the battery of an electric car requires at least 3000 cycles per 10 years. As a relatively expensive component, the lifespan of the battery is very important to ensure both the performance of the vehicle and the interests of the car owner, in order to promote the market. At present, among the electric vehicles of various car companies around the world, only BYD (002594, stock bar) "Qin", which went public last year, has achieved a lifetime battery cell warranty.
The lifespan of a battery, also known as its cycle life, is not simply a number given by battery parameters. The cycle life of a battery is closely related to its cycle state, such as discharge rate, charge rate, temperature, etc. The typical cycle life obtained from battery laboratory data is obtained at a constant charge discharge rate of 0.3C and a constant optimal temperature of 20 degrees Celsius. However, in the actual process of using the car, the magnification and temperature are both non constant. That's why the actual lifespan of batteries in laptops, mobile phones, and electric scooters is far less than the data provided by manufacturers. However, for small and medium range pure electric and long range dual-mode hybrid vehicles, due to the relatively small number of batteries carried, the requirements for their discharge will be higher, and the impact on their lifespan will be greater.
For example, the A123 lithium iron phosphate battery typically has a cycle life of over 3000 times. However, the A123 lithium iron phosphate model aircraft battery, when used at a charging rate of 10C and a discharging rate of 5C, has a shortened lifespan of only 600 times in the laboratory, compared to only about 400 times in actual use, indicating the impact of discharging rate on lifespan.
Taking BYD "Qin" as an example again, only a 13KWH battery drives a motor with a peak power of 110KW. It can be calculated that when "Qin" is fully charged, its maximum discharge rate is as high as 8.4C. Especially when 'Qin' has only 50% battery capacity, its maximum discharge rate can reach 18C. If the battery level is even lower, the discharge rate will exceed 25C, which will greatly shorten the battery life.
Looking at the Tesla with a P85 kWh battery and a maximum power of 310KW motor, it looks very large, but in fact, the battery discharge rate is only 4C. At only 30% battery capacity, the maximum discharge rate is only 10C. Moreover, Tesla's high-capacity batteries greatly prevent the battery from being subjected to high-power discharge.
By simple comparison, it can be seen that BYD batteries have superior high rate discharge life.
4、 Cost
The cost is very easy to understand, and in order to be widely popularized, there must be a cost advantage, which has already been calculated in the first article of this series. Small range pure electric or hybrid electric vehicles require reducing the amount of onboard batteries to save on battery cell costs, as well as lowering the cost of battery packs and protective equipment. Therefore, we found that although Tesla's battery cell costs are relatively low, the overall cost remains high.
5、 Energy density
Energy density, as the name suggests, refers to the amount of energy that a unit weight of battery can hold. Energy density is usually an important indicator for judging battery performance, but in my analysis system, energy density is not very important in battery performance indicators.
There are two reasons:
1. Energy density must be combined with other properties. For example, the energy density of lithium iron phosphate batteries is indeed not high. However, due to its safety, stability, and high temperature resistance, batteries composed of lithium iron phosphate as the battery cell are extremely simple and do not require too many protective auxiliary equipment. Although Tesla's ternary battery has a high cell density, its safety is poor and it cannot withstand high temperatures, so it must be combined with a complex battery protection device, which increases the weight of the car. There are reports that after a continuous combustion accident, Tesla is preparing to thicken its battery protection equipment, which weakens the energy density advantage of ternary batteries.
2. Weight has little impact on cars, especially for the mainstream trends of hybrid and small range pure electric vehicles in the future. We can imagine comparing batteries with energy densities of 130 kWh/kg and 200 kWh/kg. Even with a maximum total power of 80 degrees, the weight difference between the two batteries is only 200KG.
This has a low impact on a car weighing nearly 2 tons.
Therefore, although the energy density of a battery is naturally better, it is not necessary to deliberately pursue the maximum. Especially the higher the energy density, the more unstable it is, which is a basic knowledge. As long as it reaches a sufficient level, energy density is not too important.
