As we all know, the cost of batteries for new energy vehicles currently accounts for about 40% of the total vehicle cost. Most of the reasons why the price of new energy vehicles remains high also have to do with cost. battery life is too high. If new energy vehicle manufacturers want to improve their competitiveness, they must improve vehicle performance while reducing costs. At present, the battery, which represents the largest cost of the vehicle, has become its main focus.
In the first half of this year, due to the popularity of new energy mini cars such as Hongguang MINI EV, which are mainly equipped with lithium iron phosphate batteries, and many mainstream manufacturers have launched models equipped with lithium batteries. iron phosphate battery packs, resulting in a significant increasee of the use of lithium iron phosphate batteries compared to before. As of August this year, the installed volume of lithium iron phosphate batteries reached 7,214.5 MWh, which is 1.4 times that of ternary lithium batteries. The spring of lithium iron phosphate batteries has arrived.
The lithium iron phosphate version of the Xpeng G3 was delivered in the second quarter of this year, and the Xpeng P7 also launched a model with a lithium iron phosphate battery.
Similarly, the Tesla Model 3 and Model Y also launched models equipped with lithium iron phosphate batteries. At the same time, Tesla plans to increase the number of vehicles equipped with lithium iron phosphate batteries to two-thirds of its overall production.
Finally, BYD also announced that it will abandon the use of ternary lithium batteries and use lithium iron phosphate blade batteries as batteries for newly produced vehicless.
It can be seen that the use of lithium iron phosphate batteries to reduce costs has become a consensus in the industry. However, the problem of poor low-temperature performance of lithium iron phosphate batteries and large SOC estimation errors has not been well solved. As a result, the user experience of vehicles equipped with lithium iron phosphate batteries has always been inferior to that of models equipped with ternary lithium batteries. In this regard, NIO chose to take into account the advantages of ternary lithium batteries and lithium iron phosphate batteries, solve the two problems of lithium iron phosphate batteries through a hybrid solution, and launched a ternary lithium iron phosphate battery of 75 kWh. ?
NIO's new 75 kWh battery is to replace the existing 70 kWh battery. Now new NIO car buyers can choose enduran batterythis standard ternary lithium iron (75 kWh) or a long-range ternary lithium battery. (100 kWh). The 70 kWh battery will no longer be available. The sale price, BaaS price, etc. of the standard ternary lithium iron endurance battery model (75 kWh) are the same as the original 70 kWh ternary lithium battery model. there will be no price increase if the quantity increases,” so let’s see how NIO achieves this.
The hybrid battery integrates lithium iron phosphate cells and ternary lithium cells in a series connection in a battery, which means that the battery is not a single cell battery in the traditional sense , but rather a battery. has a battery with two battery cells. According to different design requirements, the ratio of lithium iron phosphate batteries and ternary lithium batteries can be 5:1, 3:1 or 1:1 and other ratios. Currently this 75k batteryWh is mainly based on lithium iron phosphate batteries. heart.
Compared with lithium iron phosphate battery, this hybrid batteryThe battery life loss at low case temperature is reduced by 25%, and the SOC estimation accuracy is consistent with that of ternary lithium, with an error less than 3%.
Compared to the existing 70 kWh battery, through the use of a new generation of CTP technology, the energy density increased by 14%, reaching 142 Wh/kg, and the capacity has increased by 5 kWh, giving the vehicle longer battery life.
1 The intelligent arrangement of the battery cells
Due to the use of CTP technology, the battery does not have a real module . Weilai will The ternary lithium batteries are arranged in the four corners of the battery, and the lithium iron phosphate batteries are placed in the centerdrums. Why is it organized this way?
In fact, the parts of the battery that lose the most heat are the four corners of the battery. In a low temperature environment, the temperature of the four corners of the battery will be significantly lower than that of the four corners of the battery. The core temperature of the battery, so NIO will not be affected by low temperature. Large ternary lithium batteries are arranged in the four corners, and the "cold-sensitive" lithium iron phosphate batteries are arranged in the battery where the temperature is high. the changes are not so obvious.
In addition, NIO has also added low thermal conductivity insulation materials around each battery cell, which is equivalent to covering each battery cell with a "small quilt", further reducing heat losses.
Such a design not only reduces the disthermal sipation, but the battery can also generate its own heat. NIO also features PTC heating sheets on the edges of the three battery shells to enable active heating in extremely cold environments. It uses active radiant thermal compensation to increase the operating temperature of the battery and reduce the negative effects of low temperatures. temperature environments on the impact of the battery, thereby reducing the loss of vehicle range in winter. ?
2 Accurate SOC Estimation
The word “SOC” may sound unfamiliar. You can understand it as the amount of energy the battery has. The problem of "cold sensitivity" of lithium iron phosphate batteries has been solved, but there is another annoying problem with lithium iron phosphate batteries: SOC cannot be estimated accurately. Many people may have faced suchkilling in which their cell phone suddenly loses power and cannot be turned on. He still had 20% power left in the last second, but then it turned off as soon as he answered the call. In fact, similar situations also exist in electric vehicles. Besides the anxiety about battery life and energy replenishment that car owners sometimes feel when driving electric vehicles, a more annoying problem is that the remaining mileage display was previously inaccurate. showed that the remaining range was still 100 km. As a result, I suddenly lost a lot of cruising range after walking not far. This experience is indeed quite bad. The final analysis is that the SOC estimation error of the battery pack is large and the SOC estimation error inherent in lithium iron phosphate batteries is greater.larger than the error in estimating the SOC of ternary lithium batteries.
Here, NIO reduced the power estimation error to less than 3% through innovations in software algorithms and hardware applications, reaching the level of ternary lithium batteries. The specific implementation plan is that since the corresponding relationship between the voltage of the ternary lithium battery and the SOC is more obvious and accurate than the corresponding relationship between the voltage of the lithium iron phosphate battery and the SOC, Weilai chose to use the optimal voltage. Tilted section of the ternary lithium battery to calibrate the entire cell of the lithium iron phosphate battery. The entire range reduces the SOC estimation error of the entire battery at the batteries at ternary lithium, which makes the display of the vehicle's remaining mileage more accurate and improves the user experience.
TheThe biggest advantage of this ternary lithium iron phosphate hybrid solution is that it uses the lithium iron phosphate battery to have better temperature stability than the ternary lithium battery and reduces the thermal insulation cost of the battery. Compared to The capacity of all lithium iron phosphate batteries can be larger, but two sets of BMS are needed to manage the batteries, and the required technology is more complex. If NIO just wants to reduce costs, it can use lithium iron phosphate batteries directly, just like Xpeng, Tesla and BYD mentioned at the beginning of this article, which directly launch models equipped with lithium iron phosphate battery packs. But NIO didn't do it. My analysis is as follows:
1. According to NIO's current battery replacement policy, the volume of the existing battery cannot be changed, although lithium batteries ternary of 70 kWh from NIO is not used. CTP technology. However, due to the advantage of high energy density of ternary lithium batteries, even if lithium iron phosphate batteries use PTC technology, they cannot achieve a capacity of 70 kWh. Users will not accept a new battery. The capacity of the pack is less than that of the pack. old battery.
2. Or is it because of NIO's battery exchange policy that the experience of new battery packs cannot be too different from that of old battery packs, so old battery users will only use not the battery exchange service? NIO's battery exchange policy cannot be maintained. Therefore, the low temperature performance of the lithium iron phosphate battery and the ability to accurately estimate the remaining mileage are the best experiences for users.Weilai readers and