Prospect Analysis Of Lithium Batteries Replacing Lead-acid in The Field Of Automotive Batteries

    Lead-acid batteries are currently the main power source for SLI in motor vehicles, and they have also been given many other applications. The advantages of lithium batteries as SLI batteries instead of lead-acid batteries mainly lie in their longer life and higher energy density. In terms of safety, the new European battery regulations on the use of restrictive materials in vehicles are considered, as well as cost, design and test specifications. The life cycle and recycling of the two batteries are also taken into consideration.

1. Battery replacement

    Over the years, the chemistry and manufacturing standards of lead-acid batteries have been adapted to new power requirements and challenges relatively quickly by adjusting additives and improving existing manufacturing processes, rather than trying to redesign a completely new battery system. In the 1960s, the service life of a lead-acid SLI battery was about 3 years, and by 2015, as power and application requirements increase, the battery may last as long as five years or more.

    Lead-acid batteries have maintained market share, mainly because they can meet the high current required for cold ICE startup, high-temperature cycle durability, relatively high safety, and relatively low cost. If you plan to participate in this market, then these are the challenges that any new battery technology must face. In recent years, the stability of lithium batteries in terms of chemistry and manufacturing has been significantly improved, the cost has been continuously reduced, and the performance has been continuously improved. In a broader sense, compared with lead-acid batteries, the current main advantages of lithium-ion SLI batteries are their high energy density and long life.

    Lithium-ion SLI batteries have similar performance to existing lead-acid SLI batteries, and additional tests have been introduced to evaluate the stability of lithium-ion SLI batteries. Including strict safety measures, such as overcharge protection, crush or puncture type destruction tests, continuous low-temperature discharge and charging, and evaluation of the impact of lithium deposition.

2. Safety design of lithium-ion battery

    The main challenge in the development of lithium-ion SLI batteries is how safe the battery is under abuse or aging conditions, and whether thermal runaway will occur. Many tests have been conducted to prevent this situation, but not all situations are predictable. As the accident caused excessive damage to the interior of the vehicle, which may cause the battery to burn due to external or internal fires, the precautions taken will ensure that the damaged battery will not further cause sparks, thereby reducing the spread of fire after the accident. In addition, a unique factor of the battery is the internal short circuit (ISC) that may occur due to its aging. Some common conditions, such as the formation of lithium dendrites, penetrate the diaphragm to cause a short circuit, which causes the diaphragm to shrink due to heat and cause a large-area short circuit. Another challenge for standardized battery testing is that the external structure of lithium-ion batteries can be cylindrical, pouch (soft pack) or square. Therefore, each battery type requires a different mechanical test procedure. These techniques can be used to guide the understanding of the correlation between safety testing and lithium-ion SLI batteries.

3. SLI battery design

    In the design of SLI batteries, there are a variety of electrode materials and battery combinations to choose from. However, when the overall battery voltage is limited to a typical 12V, it is possible to replace the existing lead-acid battery in this case. Currently, only a few batteries connected in series can reach the correct battery voltage.

    In addition to the requirement to obtain a battery voltage close to 12V, other factors such as easy availability in the consumer market need to be considered. Compared with standard lead-acid batteries, these materials can make cost-competitive SLI batteries. The cathode materials of lithium-ion batteries can be divided into layered, spinel and olivine types. The anode material is mainly carbon. In addition to considering the compatibility of cathode and anode materials to provide the correct battery voltage and power capacity, the first of lithium-ion batteries The three important components are its electrolyte. For most commercial batteries, organic liquid electrolytes are used together with soluble lithium salts, which can provide the required lithium ion conductivity. The most common salt currently used is LiPF6.

    In BEV, the 12 V lithium-ion SLI battery can be used to maintain the vehicle's on-board electronic system when the vehicle is not driving. The use of lead-acid SLI batteries in this application is not ideal because it is usually designed for high power and It is not necessarily suitable for the application scenarios of deep low current discharge. In this regard, lithium-ion SLI batteries just make up for the shortcomings of lead-acid SLI batteries.

4. Design of battery balance and battery management system (BMS)

    Unlike lead-acid SLI batteries, the challenge for lithium-ion battery technology is that they have a high recharging efficiency close to 95% and must work strictly within the battery voltage window. When lithium-ion batteries are assembled in series and charged, they can easily drift outside the battery voltage window, the active material may begin to experience irreversible phase changes, and the electrolyte may begin to decompose. This in turn increases the internal resistance of the battery, thereby increasing the unbalance effect of the battery. Therefore, battery management and monitoring of individual battery packs have become standard practices for lithium-ion modules, and they are usually built into the battery box housing. There are a large number of BMS systems on the market, many of which are tailor-made for specific lithium-ion battery chemicals. The simplest and most cost-effective charging method is to limit the charging of the series battery pack. A better method is to allow the redistribution of energy between the batteries once the battery reaches its upper voltage limit, preventing a single battery from overcharging and causing safety issues.

5. The cost of the battery

    Compared with existing technologies, one of the main challenges of lithium-ion SLI batteries is to provide consumers with a competitive price. Researchers are working hard to study the value chain issues in the manufacture of lithium-ion batteries. At present, almost 60% of battery costs are considered to be composed of inactive materials such as current collectors, separators and battery casings. The additional cost comes from solid electrolyte interphase (SEI). ) The time and energy spent in the formation process.

6. Policies and legislation

    The main drivers of technology are usually accompanied by certain national and international policies related to health and safety, followed by legislation. These usually involve the use of certain chemicals or chemical accessories that are considered harmful to humans and the environment. Especially when these harmful substances are used in vehicles, their design concept should be able to achieve "green recycling", that is, they can be Disassemble so that various materials can be reused, recycled or safely disposed of without causing any pollution to the environment.

7. Standards and specifications

    Over the decades, specifications and standards have emerged and gradually developed to adapt to the performance and safety of almost all battery applications, including SLI batteries for vehicles. On the other hand, the legislation of certain countries or regions can refer to standards when dealing with certain requirements that usually have a direct impact on the safety and health of the community and the environment. The United States Advanced Battery Alliance (USABC) has compiled a battery testing manual (Revision 2) for the U.S. Department of Energy (DoE).

8. Battery recycling

    Currently a company with certain strength in recycling lithium-ion batteries.

    The above summarizes that some large companies are actively participating in the established industrial-scale recycling process of lithium-ion batteries. The recycling capacity of the emerging recycling industry will increase at least five times in the next 7 to 10 years.

9. Conclusions and prospects

    This article summarizes some factors of replacing lead-acid SLI batteries with lithium-ion SLI batteries, which will be a gradual process in the next few years. With the massive use of renewable energy system storage, the use of lead-acid batteries will continue to grow, and the focus of lithium-ion SLI batteries will be used in mid-to-high-end ICE vehicles located in Europe, some of which are in Asia and the United States. For many small and cheap ICE vehicles, the lead-acid SLI battery will continue to be used, because the cost of replacing the battery will always be the decisive factor. In addition, the global consumer market will increase the use of "circular economy" products, which will focus on reducing environmental waste while increasing the recycling of raw materials. Although the recycling of lithium-ion batteries is still in its infancy, China, Japan and other countries have already carried out major initiatives. The United States, Australia and European countries have all demonstrated the new functions of recycling materials in lithium-ion batteries. These recycling processes will take place in the next five to five years. Perfect in ten years.