Lithium iron phosphate and nickel cobalt aluminum battery

When the motor and control technology are well-documented and mature, the most difficult situation and the biggest competition for electric vehicles come from battery technology. The future of electric vehicles represents silence and patience. But the representatives of China and the West on the cusp: BYD and Tesla have something to say.

On the early Roadster electric sports car, Tesla used a very small 18650 lithium cobalt oxide battery, which is commonly used in small appliances such as mobile phones and notebook computers, its biggest feature is its very high energy density, which is almost 170 watt-hours/kg. However, its thermal stability is also criticized at the same time, and decomposition occurs at about 180 degrees and oxygen is generated.

Later, in order to compromise energy density, power density and safety, Tesla used a modified ternary battery nickel-cobalt aluminum battery on the ModelS model, bringing the total number of batteries to more than 8,000 knots, more than 1,000 knots more than the Roadster. But the cost has dropped by 30%. Despite this, the very limited number of cycles is still a problem for the application of such batteries in electric vehicles. The battery will be dead after about three to four years, based on the charging frequency every two days.

Tesla's solution is to provide a "no fault" battery warranty policy, which means that as long as it is not caused by man-made damage or battery damage caused by a collision, you can get eight years of free warranty. And when the battery life expires, Tesla will bear the recovery and replacement of the battery. Such a policy will put a lot of pressure on Tesla with the introduction of the entry-level models and the increase in sales. This may be one of the reasons why it is preparing to build the world's largest battery factory.

In contrast, the lithium iron phosphate battery used by BYD is currently the more widely used battery. Its advantage lies in its high thermal stability. The structure is still stable at 600 °C. At the same time, because the ferric ions are not active, it is difficult to make chemical changes again. This makes the lifespan relatively long and theoretically can be larger than the whole vehicle. Life expectancy and low cost for long-term use. At the same time, the lithium iron phosphate battery has a relatively good power density, can be discharged at a large rate, and has good acceleration performance.

However, compared with the ternary lithium battery, the energy density of the lithium iron phosphate battery has no advantage, about 100~110 watt-hour/kg, which results in a shorter cruising range under the same weight conditions, and wants to achieve higher The cruising range will inevitably increase the weight of the battery and increase the cost.

In terms of comprehensive performance, not all companies have Tesla's software capabilities and battery management capabilities, so lithium iron phosphate batteries are still more optimistic and more pragmatic battery types. This may be one of the reasons why GM is preparing to use lithium iron phosphate batteries.

Because of the characteristics of the battery, Tesla has designed a very deep design on its battery arrangement, thermal management system, and battery management system to ensure that each battery unit is under supervision and its status data can be feedback at any time, deal with. For a single small cell, Tesla encloses it in a steel compartment independently, while the liquid cooling system can specifically cool each cell, reducing the temperature difference between each other and reducing the self-ignition of the battery risk.

Tesla exposed the accident, mainly due to a partial short circuit of the power line caused by the battery pack puncture. At present, Tesla cannot solve the situation that the battery pack is burnt and exploded under the extreme damage of the impact force, but the high-intensity protection has won more time for the owner to escape.

In fact, this is almost a potential common hazard of electric vehicles, and it puts very high demands on the function of the battery management system. In addition to daily regulation of battery temperature and working conditions, it is also necessary to cut off the high voltage line immediately when the temperature changes rapidly or an extreme collision occurs. The upgrade of the thermal management system and the battery management system will also shorten the battery charging time and bring higher charging efficiency.

In addition, how to ensure battery charging and use efficiency in low temperature environment is a problem that enterprises engaged in research and development and production of electric vehicles need to solve.

In addition, it is necessary to mention that Tesla has always promoted pure electric vehicle products, and its high-end route, from high to low, has also reflected that the market is not enough for the inclusiveness of electric vehicles.

In the future, BYD intends to promote the "Double-engine dual-mode" car, in fact, in order to promote the plug-in hybrid car as a transitional product before the electric market is truly opened. Compared with traditional gasoline vehicles, hybrid vehicles are more fuel efficient and reduce the amount of batteries. Considering the policy subsidies for new energy vehicles, the cost of purchasing cars has also been lowered. This is in line with BYD's popularization of products.

The page contains the contents of the machine translation.