I. Car manufacturers' requirements for battery performance
The basic requirements for battery cells include: energy density (driving range), safety, fast charging, cost, lifespan, and size compatibility.
1. Energy density
According to my country's automotive power lithium battery technology roadmap, by 2020, the system-level energy density should reach 250Wh/kg, the cost should be reduced to less than 1 yuan, and the driving range should reach more than 400km. There are not many mature material systems to choose from. At present, it is basically confirmed that high-Ni ternary materials and silicon-based anode materials or corresponding high-voltage materials will be used.
The actual goals of major domestic and international battery companies are as follows:
Increased cell energy density, lightweight and compact pack design, and improved system energy utilization efficiency have made significant contributions to increasing driving range and reducing costs.
2. Cell safety performance
The rapid increase in battery cell energy density presents new challenges to battery cell safety, and the market urgently needs large-scale product deployment. Furthermore, investment in system safety design should be strengthened, and product integration and application safety should be achieved through multi-level and multi-dimensional design from a system perspective.
3. Fast charging feature
Based on advancements in charging infrastructure and battery technology, it is believed that 30-45 minute fast charging will become the mainstream technological requirement, while 10-15 minute fast charging will be researched and applied in certain areas. Battery swapping is primarily seen in taxi operations, where the current level is 3-5 minute fast swapping.
4. Battery cost and size compatibility
Advances in materials technology, large-scale production, standardization, reduced vehicle energy consumption, and tiered utilization are all contributing to cost reduction in batteries. Standardization minimizes development costs and is also a crucial foundation for tiered utilization. In the future, vehicle manufacturers will define module specifications (such as the dimensions of VDA or new national standard power batteries for electric vehicles), arranging batteries within these specifications to facilitate cross-platform applications and recycling. With the increasing demand for optimized vehicle layout, skateboard-style battery packs are being placed on the battery chassis, with increasingly stringent Z-axis requirements, further reducing the height from 120mm to 100mm, and optimizing the cell height from 91mm to 80mm.
5. Lifespan
The battery life should meet the warranty commitment of 10 years or 160,000 km, with a life target of 10 years and 240,000 km. As the vehicle's driving range increases, the battery cycle life will be relaxed accordingly.
II. Automakers' Development Process for Power Lithium Batteries
Taking BAIC as an example, the overall development process based on the whole vehicle is as follows:
BAIC's EVDP (Electric Vehicle Development Process) workflow prioritizes the development and verification of each subsystem before the parent system to ensure product development reliability. This is based on the assumption of simultaneous development of the battery system and battery cells. Depending on the actual development situation, more mature battery cell products will be prioritized.
SAIC Motor divides the process into four stages: pre-screening, battery confirmation and evaluation, cell confirmation and evaluation, and system verification. Each stage has strict testing procedures and controls.
1. Selection of cell type
From the perspective of positive and negative electrode materials, battery cells currently include NCM (111, 523, 622, 811), LCO, LFP, LMO, LTO, etc. Automakers need to select cells based on energy density, power characteristics, cycle life, and safety. Additionally, based on battery packaging shape, they can be divided into cylindrical, pouch (laminated and wound), and prismatic (laminated, wound, parallel wound). The key characteristics of each type of battery cell are summarized below:
2. Battery Testing and Evaluation System
The evaluation system comprises three horizontal and four vertical dimensions. The three horizontal dimensions are: key components centered on battery cells, battery modules, and battery systems, with different testing and evaluation methods implemented at different development stages. The four vertical dimensions are: four types of testing—accreditation testing, calibration testing, field research testing, and virtual verification—covering nearly 158 verification items, including 33 items related to system thermal safety, electrical safety, and mechanical safety. Thermal safety includes 11 sub-items and 29 sub-items; electrical safety includes 15 sub-items and 33 sub-items; and mechanical safety includes 17 sub-items and 35 sub-items.
3. Accreditation Experiment
The five-step, four-level cell management method includes technical status management, process and material information filing management.
We implement tiered development and management of battery cells, from external characteristics to internal materials and processes, to assess and manage the feasibility of applications from technical feasibility to mass production feasibility.
4. Calibration Experiment
This is the process of verifying the vehicle's power performance, economy, environmental adaptability, durability, thermal balance, and SOC algorithm.
5. Topological research and experimental verification
Battery lifecycle performance evaluation
Full vehicle wading through high water level
Research on electrical safety distances in high humidity environments
High-altitude drop test
Continuous fire test
Cutaway Test of Power Lithium Battery System
6. Virtual simulation verification
During the product development phase, virtual verification conducted a total of 40 simulation analyses across two categories (structural and thermal) and two levels (module-level and system-level).
