By Austin Weber // Senior Editor // webera@bnpmedia.com

Lithium-Metal Battery Recharges in Minutes

AV/EV tech trends

Engineers at Harvard University have developed a lithium-metal battery that can be charged and discharged thousands of times and recharged in a matter of minutes.

They built a postage stamp-sized pouch cell version of the battery, which is 10 to 20 times larger than the coin cell made in most university labs. The battery retained 80 percent of its capacity after 6,000 cycles, outperforming other pouch cell batteries on the market today.

“Lithium-metal anode batteries are considered the holy grail of batteries, because they have 10 times the capacity of commercial graphite anodes and could drastically increase the driving distance of electric vehicles,” says Xin Li, Ph.D., associate professor of materials science at Harvard. “Our research is an important step toward more practical solid-state batteries for industrial and commercial applications.”

One of the biggest challenges in the design of these batteries is the formation of dendrites on the surface of the anode. These structures grow like roots into the electrolyte and pierce the barrier separating the anode and cathode, causing the battery to short or even catch fire. Dendrites form when lithium ions move from the cathode to the anode during charging.

Li and his colleagues stop dendrites from forming by using micron-sized silicon particles in the anode to constrict the lithiation reaction and facilitate homogeneous plating of a thick layer of lithium metal.

When lithium ions move from the cathode to the anode during charging, the lithiation reaction is constricted at the shallow surface and the ions attach to the surface of the silicon particle but don’t penetrate further.

“In our design, lithium metal gets wrapped around the silicon particle, like a hard chocolate shell around a hazelnut core in a chocolate truffle,” explains Li.

These coated particles create a homogenous surface across which the current density is evenly distributed, preventing the growth of dendrites. And, because plating and stripping can happen quickly on an even surface, the battery can recharge in only about 10 minutes.

“Previous research had found that other materials, including silver, could serve as good materials at the anode for solid-state batteries,” says Li. “Our research explains one possible underlying mechanism of the process and provides a pathway to identify new materials for battery design.”

Recycling Project Gives Old Electric Motors a New Life

An R&D initiative in Germany is exploring new ways to recycle and reuse electric motor components. The Fraunhofer Institute for Manufacturing Engineering and Automation (Fraunhofer IPA) is in charge of the REASSERT project, working with partners such as Schaeffler and other manufacturers.

The goal is to develop a prototype electric motor that can easily be disassembled for the circular economy. The project partners define “reuse” as reusing the entire motor for secondary use and repair as the replacement of defective components and assemblies. In “remanufacturing,” all components are disassembled, cleaned, reconditioned and reassembled.

“Innovative value retention strategies offer significant potential for emission reduction in terms of sustainability,” says Julian Grosse Erdmann, an engineer at Fraunhofer IPA working on the project. “Reuse, repair, remanufacture and raw material recycling…are key elements for a circular economy, enabling the reduction of natural resource consumption and minimization of waste.”

According to Erdmann, the raw materials used in electric motors have a bigger carbon footprint compared to a traditional internal combustion engine. Because of this, it is crucial to extend the use phase of these motors.

At present, recycling of raw materials is the established value retention strategy. Through either manual or automated recycling methods, materials such as aluminum and copper are recovered. Electric traction motors are disassembled, shredded, sorted into individual material fraction and melted down. However, the recycled material, which is often contaminated, can no longer be used for motor applications, and individual components and assemblies are destroyed.

“We want to establish a closed-loop system in which valuable resources are reused in order to eliminate dependency on raw material imports and to minimize raw material extraction,” explains Erdmann. “With these strategies, fewer raw materials like rare earths and copper are needed.”

The REASSERT project involves establishing a complete process, each step of which boasts its own demonstrator and test rig, from inbound inspection for motor classification to disassembly, demagnetization, cleaning, component diagnosis and remanufacturing, all the way through to reassembly and end-of-line testing, where the motor’s functionality is assessed.

“For instance, during this process, a motor housing with minor wear might be classified for reuse and, if necessary, reconditioned using machining processes to ensure functionality,” Erdmann points out. “Depending on the chosen value preservation strategy, different process steps and chains are involved, so the effort for reconditioning may vary.

“An example of one of the challenges of this would be disassembling and reusing the magnetic materials from motors,” notes Erdmann. “A rotor with permanent magnets is difficult to disassemble into its components even in a manual disassembly process, due to the coating and bonding of the magnets. Here, the goal is to establish nondestructive disassembly methods.”

An AI tool developed as part of the project helps to select the best value retention strategy for a given application. It has access to the product and process data for the electric motor, which are saved in a digital twin.

New Cathode Manufacturing Method Could Boost the Range of EV Batteries

Cathodes for conventional EV batteries use a mix of lithium nickel manganese cobalt oxides (NMC). When more nickel is incorporated into a cathode, it greatly increases the battery’s ability to store energy, and thus, the range of the EV.

However, high-nickel NMC cathodes formed using the standard method are agglomerated into polycrystal structures that are rough and lumpy. The bulbous polycrystal fissures are prone to splitting apart, causing material failure. This renders batteries made using these nickel-rich cathodes susceptible to cracking; they also begin to produce gases and decay faster than cathodes with less nickel.

One way to fix this problem is to convert that lumpy, polycrystal NMC into a smooth, single-crystal form by eliminating the problematic boundaries between the crystals. But, this involves mixing a metal hydroxide precursor with lithium salt using a multiple-step heating process.

To address these challenges, engineers at Pacific Northwest National Laboratory (PNNL) developed a preheating step that changes the structure and chemical properties of the transition metal hydroxide. When the preheated transition metal hydroxide reacts with lithium salt to form the cathode, it creates a uniform single-crystal NMC structure that looks smooth, even under magnification.

“The one-step heating process of precursors seems straightforward, but there is a lot of interesting atomic-level phase transition involved to make the single-crystal segregation possible,” says Yujing Bi, Ph.D., a PNNL engineer leading the project. “It is also convenient for industry to adopt.”

The first prototype battery equipped with the scaled single crystals was stable, even after 1,000 charge and discharge cycles. When the researchers looked at the microscopic structure of the crystals after 1,000 cycles, they found no defects and a perfectly aligned electronic structure.

Bi claims that the synthesis method for the single-crystal, nickel-rich cathode is cost-efficient and easy to scale up, because it is a drop-in approach that allows cathode manufacturers to use existing production facilities to conveniently produce single-crystal NMC811 and even cathodes with more than 80 percent nickel.