lithium 18650 li ion battery

lithium 18650 li ion battery: high safety and low energy density coexist

Behind the frequent spontaneous combustion of power batteries: Can lithium titanate batteries enter the passenger car market?

On the evening of April 21, a Tesla Model S caught fire in a garage in a residential area in Shanghai and affected nearby vehicles; on April 22, a Weilai ES8 also caught fire... Multiple electric vehicle spontaneous combustion incidents have pushed electric vehicles to the forefront again. Some netizens even broke the news that electric vehicles will be treated "unfairly" by property management when applying for parking spaces.

So far, Tesla and other companies have not made an official explanation for the cause of electric vehicle spontaneous combustion. Eo Auto talked with Li Haibo, co-founder and chief business officer of Guochuangcheng on this issue. In his opinion, Tesla has reached a very high level in the three-electric system, but its products have more than once had spontaneous combustion incidents, which is related to its battery technology route itself.

The negative electrode material of the ternary lithium battery used by Tesla is a carbon-based material. In Li Haibo's opinion, the carbon negative electrode battery itself is an inherently unsafe battery. Last year, Academician Ouyang Minggao of Tsinghua University published a paper pointing out that the positive electrode of the power battery in the charged state will release oxygen and only generate less heat, that is, the battery will not be ignited by the heat generated by the internal short circuit; but when there is a negative electrode, the strongly reducing negative electrode (carbon-based material) will consume the oxygen generated by the positive electrode and generate a lot of heat, which will eventually cause the entire battery to have thermal runaway.

Generally speaking, carbon-based materials are flammable in themselves, and the lithium embedded in carbon-based materials will form the compound LiC6, which has properties close to lithium and can directly self-ignite in the air. Therefore, the safety shortcoming of lithium batteries is due to the existence of carbon-based negative electrode materials, which is a safety hazard of the material itself.

Therefore, Guochuangcheng chose to enter a new power battery field: lithium 18650 li ion battery.

lithium 18650 li ion battery: high safety and low energy density coexist

Today, ternary lithium and lithium iron phosphate batteries have occupied more than 90% of the market in my country's power battery industry. As a new power battery manufacturer, Guochuangcheng did not enter the current mainstream market, but chose to focus on lithium titanate batteries. Of course, this is also because lithium titanate batteries have certain advantages.

First of all, compared with ternary lithium or lithium iron phosphate batteries, which can only rely on external control systems to ensure safety, lithium titanate batteries are safe at the material level. Li Haibo told EoAuto that due to the use of spinel structure lithium titanate, the material of this structure has almost no volume change during the process of lithium insertion and removal, and the lithium insertion potential is relatively high, so even in the later stage of low temperature, high rate charging and other harsh use environments, lithium titanate batteries will not reach the precipitation potential of metallic lithium, reducing the probability of forming lithium dendrites and the risk of short circuit.

In addition, even if a short circuit occurs internally, the temperature of the lithium 18650 li ion battery can only rise to 60°C at most, which does not reach the temperature level of battery combustion. The main component of lithium titanate is titanium oxide, which does not burn by itself. According to Li Haibo, the heat released by the combustion of the graphite negative electrode after lithium insertion is about 10 times that of the lithium titanate negative electrode. "Even if the lithium 18650 li ion battery burns, it will burn slowly and will not explode," he added.

In addition to high safety, Li Haibo said that lithium titanate batteries also have three other advantages: first, long service life, high-rate charge and discharge times can reach 10 times or even more than 20 times that of other types of batteries; second, wide temperature range, can work normally under low or high temperature conditions; third, can achieve high-rate charge and discharge, lithium titanate batteries can be fully charged in 10 minutes, or even 5 minutes, which takes much less time than ternary lithium batteries of 1 hour.

Given so many advantages, why do mainstream automotive products in my country not use lithium titanate batteries? Because compared with their competitors, the energy density of such batteries is too low. The energy density of lithium titanate batteries that Guochuangcheng can currently mass-produce is 100Wh/kg, which is about 70%~80% of lithium iron phosphate batteries and only 50%~60% of ternary lithium batteries. Taking the Tesla Model S as an example, the car has a range of more than 500 kilometers, but if it is replaced with a lithium 18650 li ion battery, it may only run 300 kilometers. In addition, the cost of lithium titanate batteries is also higher than that of ternary lithium batteries. Therefore, passenger car manufacturers, which mainly consider energy density and driving range, have abandoned this battery category.

Where is the market for lithium titanate batteries?

Although Guochuangcheng was only registered in November 2016 and the batteries it produced were not officially put into production until the end of 2018, according to Li Haibo, the company's team members have been engaged in the research and development and production of lithium titanate batteries for more than 10 years. They only focus on the research and development of this type of battery because they see a considerable market opportunity.

"From the current customer feedback, it is very positive," said Li Haibo. At present, Guochuangcheng has reached a bulk purchase agreement with some rail transit companies, and has won some orders in the field of new energy mining vehicles, and also has customers in logistics and other fields.

What these customers have in common is that they regard safety as the core demand and basic threshold, and at the same time need to fully consider the economy and battery life. According to Li Haibo, the battery cell of lithium 18650 li ion battery can achieve a high-rate cycle charge and discharge life of 50,000 times, which far exceeds the service life of the whole vehicle. In contrast, the high-rate charge and discharge life of lithium iron phosphate batteries and ternary lithium batteries is generally only a few hundred times, and even low-rate charge and discharge can only achieve thousands of cycles. Since the vehicles of Guochuangcheng's customers are larger in size and have more space to load batteries, the requirements for energy density are relatively low.

In addition, Li Haibo said that plug-in hybrid trucks over 12 tons have also been included in the list of national policy subsidies for new energy vehicles this year, which is stimulating Guochuangcheng to develop in this field. At the same time, he also said that the company is actively communicating with some bus manufacturers and heavy machinery manufacturers. Bus manufacturers are attracted by the advantages of lithium titanate batteries in high-rate charge and discharge and long life, while heavy machinery companies are attracted by the high-rate charge and discharge and wide temperature range characteristics of such batteries. In addition, Guochuangcheng has also actively promoted the energy storage market. Due to its high-rate performance, lithium titanate batteries have a lot of room for development in energy storage frequency modulation.

According to Li Haibo, in the long run, Guochuangcheng also has plans to enter the passenger car market. With the outbreak of multiple spontaneous combustion incidents, it is still unknown whether passenger cars will continue to consider energy density and long driving range as the first consideration in the future; in the extended-range electric vehicle market, the characteristics of lithium titanate batteries can solve both safety and mileage anxiety issues; in addition, it is expected that in the next 2-3 years, the 48V start-stop system will become the standard for passenger cars, and lithium titanate is also one of the best choices for start-stop batteries.

Li Haibo said that for the time being, the most urgent matter for Guochuangcheng is to expand the production capacity of its factories. The company's existing production capacity is far from meeting the needs of existing orders. "We are very optimistic about the lithium 18650 li ion battery market." He added.

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