Expert Insights from a Lithium-Ion Battery Developer: Three Essential Aspects to Focus on in Battery Development

How to Increase Energy Density

"Battery capacity is determined by two main factors: the materials used and the battery structure. Therefore, the best materials and structures vary depending on each company's design philosophy and use cases. This is the current state of the battery industry," says Mr. Yajima.

For instance, the cathode materials used in lithium-ion batteries often include NMC (Nickel Manganese Cobalt), known as ternary materials for its high energy density. This is one of the primary reasons for its widespread use. On the other hand, LFP (Lithium Iron Phosphate) excels in safety, lifespan, and cost-efficiency, but its energy density does not match that of NMC.

"Various materials other than graphite are being researched for anodes."

The choice of anode material combined with the cathode material is also a significant factor in determining battery capacity. While graphite is currently the predominant material, there are other anode materials aimed at higher capacities. Silicon, for instance, holds promise for achieving over ten times the capacity of graphite and is gaining attention as an anode material for next-generation batteries. However, using silicon as an anode material causes the anode to expand in volume compared to a graphite-only anode, leading to battery degradation. Therefore, a method involving the partial addition of silicon to graphite anodes is being considered. "This approach is quite reasonable", says Mr. Yajima.

"By increasing the battery pack's space utilization, similar to the blade batteries adopted by BYD, it is possible to achieve energy density comparable to NMC even with LFP."

Not only the materials used but also how battery cells are arranged is a crucial factor related to battery capacity. In the Blade Battery system, which is a type of Cell-to-Pack method, the battery cells are arranged on blades with minimal gaps, making it challenging to ensure safety through spatial separation. This is compensated by the inherent safety of LFP (Lithium Iron Phosphate) materials.

Besides Cell-to-Pack, there are many other types of battery structures. The choice of materials and structures depends on each company's design philosophy and use cases. "There is no single correct answer, which is the current state of the battery industry," explains Mr. Yajima.

"Above all, safety is paramount, including preventing ignition and fire spread."

"Above all else, ensuring safety is an absolute requirement. In order to meet these requirements, we must select materials, consider the structure, and prepare for emergencies in a design that takes every precaution possible."

To prevent battery-related fires in EVs, which must never occur, companies are devoting significant efforts to safety measures. International standards and regulations require various tests for heat dissipation, impact, collision, and fire prevention. Batteries are designed with structures for cooling and heat dissipation, as well as impact absorption, to meet these standards and regulations.

Although structural design and material selection aim to prevent ignition, "it is equally important to consider how to prevent the spread of fire in the unlikely event that an unavoidable battery fire occurs," Mr. Yajima points out.

"For instance, if a mother and her two children are in the car and a battery fire is detected, it might take five minutes for the mother to get the children out of the car by herself. In this case, we need to prevent the spread of fire in the EV for at least five minutes," he explains.

For example, under China's GB standards, it is required that the battery should not catch fire within five minutes of the battery management system issuing a warning to ensure the driver has time to escape if the battery experiences thermal runaway. To achieve this, the design should include structures that limit the fire's intensity by preventing the supply of oxygen inside the battery, and fire-retardant materials around the battery to slow down the spread of fire.

The ability to secure materials significantly impacts the production capacity of EVs.

As the demand for EVs increases, a major concern when attempting to boost battery production is securing materials such as lithium, nickel, cobalt, manganese, and graphite. For example, approximately 50% of cobalt reserves are located in Congo, and much of the refining processes are carried out in China, leading to a concentration of resources in specific countries.

"The concentration of resources underscores the significant importance of recycling materials used in batteries."

In countries like Japan that depend on imported resources, it is extremely important to reuse the resources that are acquired, he argues. From a cost perspective, recycling cathode materials, which make up a significant portion of battery costs, is highly beneficial.

In addition to recycling, diversifying resource acquisition from various countries rather than relying solely on specific nations can also be beneficial in stabilizing resource supply and minimizing risks associated with international geopolitics.

EVs play a central role in the automotive industry, which is undergoing what's being called a "once-in-a-century transformational period". NAGASE supports the future of EVs with products and technology as research and development progresses across many aspects like battery design, safety, and materials.