Currently, most pure electric vehicles in my country's new energy vehicle market use ternary lithium or lithium iron phosphate batteries. Although their energy density has significantly improved compared to lead-acid and nickel-metal hydride batteries, they still fail to alleviate consumers' range anxiety. Undoubtedly, the main obstacle to the industrialization of new energy vehicles at this stage is the bottleneck in power battery technology. However, while increasing battery capacity is currently difficult, weight reduction is a feasible solution.
■Can the density of lithium-ion batteries be increased further?
Currently, both ternary lithium batteries and lithium iron phosphate batteries are basically composed of four key components: the positive electrode, the negative electrode, the electrolyte, and the membrane. An anonymous battery research expert told reporters that it is unlikely that lithium batteries based on these four components will achieve further increases in energy density and be commercially viable. In fact, while the energy density of power battery modules reached 300Wh/kg in 2020, five years later, a next-generation power battery suitable for industrialization has yet to emerge.
Miao Wenquan, deputy director of the Shanghai Motor Vehicle Inspection Center, believes there are many technical approaches to improving the specific energy of power batteries: First, process advancements. Battery process design is now relatively mature, leaving little room for further improvement in specific energy. Second, improvements in material performance. Limited by their inherent physicochemical properties, lithium-ion power batteries using lithium iron phosphate and ternary lithium as cathodes and carbon materials as anodes are unlikely to achieve significant breakthroughs in energy density. Third, new materials and systems. Developing high-energy-density new materials and new power battery systems are the main ways to significantly improve the specific energy of power batteries in the future. "It often takes many years for a new technology to go from the laboratory to application," Miao Wenquan said. He believes that 2020 is not a distant future, and there are currently no definitive solutions. Only a handful of next-generation power battery systems can achieve the aforementioned goals. He revealed that Japan and South Korea are currently researching gel batteries, a new type of battery without electrolyte and separator, which could potentially bring about a qualitative change in batteries, but there is no news of industrialization yet.
■ Reducing the load on the battery is a feasible approach
If battery energy density cannot be effectively increased at this stage, could we consider improving energy density by reducing the overall weight of the battery pack? Dr. Zhang Minyu of the China Battery Industry Association told reporters that this approach is entirely feasible. She stated that in a power battery pack, the weight of the battery cells generally accounts for between 1/3 and 2/3, with the remainder consisting of circuit boards, casings, and other components. If the weight of these components is effectively reduced while maintaining the current energy density of the battery cells, the overall energy density of the battery pack will see a significant increase.
Around 2010, power battery packs often used metal casings due to safety and other requirements, resulting in very low overall energy density. Later, after switching to polymer casings, the energy density improved significantly. Zhang Minyu stated that battery pack energy density is a systemic issue. Increasing cell energy density is a direct approach, but optimizing cell placement, circuit planning, and reducing casing weight to lighten the load on the battery are also effective methods for improving battery energy density.
In practical applications, reporters learned that the lower battery box of the BAIC New Energy EV200 model uses aluminum alloy, while the upper cover uses composite materials, effectively reducing weight by tens of kilograms. Wang Kefeng, Deputy General Manager of BAIC New Energy, stated that reducing the overall weight of the battery can achieve vehicle weight reduction, which is an effective way to improve the energy density of the battery box. He also noted that replacing materials with lighter ones generally leads to increased battery costs, and BAIC New Energy is currently accelerating its research in this area, striving to apply lighter, stronger, and lower-cost materials.
■ Future battery development and weight reduction in parallel
According to the goals mentioned in the "Energy-Saving and New Energy Vehicle Industry Development Plan (2012-2020)" issued by the State Council, the energy density of power battery modules should reach 150Wh/kg this year (equivalent to an energy density of approximately 170-190Wh/kg for a single battery cell), and the energy density of power battery modules should reach 300Wh/kg by 2020 (corresponding to an energy density of at least 330Wh/kg for a single battery cell).
Zhang Minyu stated that to achieve the 300Wh/kg target, the development of new batteries and the reduction of battery pack weight need to proceed in parallel. She explained that because power batteries are installed in vehicles, they need to undergo various operating condition tests to ensure structural safety. Replacing the steel casing with a carbon fiber casing or other materials is entirely feasible as long as the strength requirements are met. Another important indicator for battery packs is heat dissipation and heat equalization. If the battery pack overheats locally, it will lead to inconsistent internal resistance and a decrease in cell discharge capacity. Those cells that do not discharge sufficiently, in a sense, add weight to the battery pack. "Achieving a battery pack energy density of 300Wh/kg may not be achievable solely by reducing battery weight, but the role of the power battery as a system cannot be ignored," Zhang Minyu said. Wang Hewu, Deputy Secretary-General of the China EV100, stated that China is not lagging behind its foreign counterparts in power battery manufacturing. However, domestic companies lack basic research and excessively pursue high-energy-density cells. A balanced development approach is needed, focusing on reducing the weight of existing battery systems while developing new battery materials.
Battery weight reduction depends on industrialization process
Electric vehicle batteries are currently quite expensive. Taking the BAIC New Energy EV200 as an example, the battery cost accounts for almost half of the total vehicle cost. If lighter materials are used on top of this, the cost will increase further. This is the biggest reason why many automakers haven't adopted new materials yet. Furthermore, whether new materials will be accepted by consumers is another issue that automakers need to consider. With the relatively low operating costs of pure electric vehicles, consumer demand for lightweight materials is not high, which also restricts their application.
In the short term, reducing the burden on batteries is somewhat of a thankless task. Some vehicle manufacturers told reporters that only when the supply chain matures and the production and sales of new energy vehicles further increase will new materials be widely used. For new energy vehicles with only over 70,000 units sold in the first half of the year, this is indeed a stark reality. An industry expert shared a personal experience that aptly illustrates this point.
This expert, who works in research on new energy vehicles, bought an electric car. While reversing, he accidentally hit a wall, damaging the rear bumper and rear window. He took the car back to the 4S dealership for repairs, expecting a week's work, but it took a month. The repair cost shocked him; the bumper and rear window repairs alone cost over 10,000 yuan. Puzzled, the expert consulted the dealership and was told that due to low production volume at the vehicle manufacturer, there were no spare parts, and he spent most of the month waiting for them. Furthermore, because spare parts are very expensive, the repair cost was far higher than for traditional cars. The expert finally lamented, "It's all because of the low production volume."
Battery weight reduction requires accelerated industrialization, and this same applies to the entire new energy vehicle industry. In the first half of this year, the new energy vehicle market saw robust production and sales. At this rate, total sales for the year are expected to exceed 200,000 units. At this scale, the industry chain will mature further, and component costs are expected to decrease further.
As things stand, the difference between small-scale demonstration operations and large-scale market operations is far more than a simple accumulation of numbers. Automakers need to increase R&D investment to accelerate technological progress, overcome technological barriers and hurdles, improve driving range, and rapidly reduce costs, ultimately enabling this nascent industry to grow and mature in the shortest possible time.
All roads lead to Rome
Currently, the methods for improving the energy density of power batteries are relatively limited. Aside from developing new battery types, there are essentially two approaches: increasing the weight of the positive electrode active material and reducing the weight of battery pack components. The former directly increases battery energy but also introduces several problems, such as decreased safety and localized overheating. While the latter method's effect is less immediately apparent, it still achieves the same goal as the first.
Reducing the weight of components without compromising their strength is crucial. Currently, my country lags behind in battery research and application. In materials science research, we must acknowledge a gap with international counterparts, particularly in basic research. Furthermore, replacing heavier materials with lighter ones generally leads to increased costs. Given the already high cost of power batteries, it's unlikely that automakers will adopt this approach.
However, research from abroad suggests that finding a material that is strong, lightweight, and low-cost is possible. Recently, Volvo Cars announced that its electric vehicle battery lightweighting technology has entered the practical testing phase. Volvo stated that the new battery material is lower in cost and more environmentally friendly. Replacing all current electric vehicle batteries with this new material could reduce vehicle weight by more than 15%, a clearly significant improvement.
Rearranging the batteries is also an effective way to improve system energy density. For example, by researching and designing the cell size to match the overall vehicle layout, more batteries can be placed more efficiently, thus increasing the number of cells while keeping the battery pack volume the same, thereby achieving a longer driving range. In short, improving battery energy density can be achieved through various methods.
Besides long-term planning, the most pressing task for automakers is to develop more reliable and economical lightweight materials. At a time when battery technology faces bottlenecks, focusing on lightweight design principles is a significant driving force for the electric vehicle technology revolution. Regardless of the materials used in future new batteries, the materials that make up the battery pack can be largely interchangeable. While the short-term benefits may be limited, in the long run, this fundamental research will not be in vain.
