Researchers use carbon-based anodes with “bumpy” surfaces for Li-ion batteries that last longer in extreme cold

To improve the performance of Li-ion batteries in the extreme cold, researchers from Tianjin University, Beijing Jiaotong University, Karlsruhe Institue of Technology and other colleagues replaced the traditional graphite anode in a lithium-ion battery with a carbon-based anode material (O-DF) strategically synthesized to construct the Riemannian surface with a positive curvature.

The resulting 12-sided carbon nanospheres had “bumpy” surfaces that demonstrated excellent electrical charge transfer capabilities. The material exhibits a high reversible capacity of 624 mAh g^–1 with an 85.9% capacity retention at 0.1 A g^–1 as the temperature drops to −20 °C. Even if the temperature drops to −35 °C, the reversible capacity is still effectively retained at 160 mAh g^–1 after 200 cycles.

An open-access paper on the work is published in ACS Central Science.

Lithium-ion batteries (LIBs) have been universally applied in various portable electronics and electric vehicles due to a high energy density and long cycle life at room temperature, but they still suffer from poor performance at subzero temperatures, especially substantial energy and power losses, which severely limits their operations in a cold environment such as high-altitude areas and aerospace explorations as well as electric vehicles under extreme conditions.

… Up to now, various strategies have primarily focused on electrolytes and electrodes to solve the above issue via the tailoring of electrolyte structures and the introduction of electrolyte additives to reduce the freezing point and boost ionic conductivity, or the surface modification of the electrode structure to lower the charge-transfer energy barrier at the interface.

… the key to addressing the low-temperature capacity loss lies in adjusting the surface electron configurations of the carbon anode to reinforce the coordinate interaction between the solvated Li⁺ and adsorption sites for Li⁺ desolvation and reduce the activation energy of the charge-transfer process. In addition, with inspiration from the geometric architectures of carbon allotropes with positive and negative curvatures, it is expected to manipulate the electronic configurations of the surface through the transformation of hybridized orbital types generated by the response of chemical bonds to bending deformations, where the insertion of one pentagon into an sp²-hybridized hexagon lattice generates a surface with a positive curvature like a bowl, while the introduction of one heptagon or larger membered rings produces a surface with a negative curvature like a saddle.

Theoretical calculations demonstrate that the curved surfaces bind lithium with a stronger affinity than the planar surface with zero curvature, particularly the structure with a positive curvature, making it possible to accomplish the high capacity of the carbon anode in an extremely cold environment. However, the carbon anode with a positive curvature as a high capacity electrode material for Li-ion storage at low temperature has never been realized, and the underlying structure-performance relation has not been theoretically and experimentally uncovered.

—Lu et al.

To create the new material, the researchers heated a cobalt-containing zeolite imidazolate framework (ZIF-67) at high temperatures. The resulting 12-sided carbon nanospheres had bumpy surfaces that demonstrated excellent electrical charge transfer capabilities. Then the team tested the material’s electrical performance as the anode, with lithium metal as the cathode, inside a coin-shaped battery.

(a) Schematic illustration of the synthesis process of O-DF. (b–d) SEM, TEM, and the corresponding SAED images of O-DF. (e, f) HRTEM images of O-DF with different magnifications. (g) Elemental mappings of C, N, and Co for O-DF. Lu et al.

The anode demonstrated stable charging and discharging at temperatures from 25 ˚C to -20 ˚C and maintained 85.9% of the room temperature energy storage capacity just below freezing. In comparison, lithium-ion batteries made with other carbon-based anodes, including graphite and carbon nanotubes, held almost no charge at freezing temperatures. When the researchers dropped the air temperature to -35 ˚C, the anode made with bumpy nanospheres was still rechargeable, and during discharge, released nearly 100% of the charge put into the battery.

Various characterizations and theoretical calculations demonstrate that the Riemannian surface induces non-coplanar sp^x-hybridized orbitals with unsaturated coordination, where the locally accumulated charges reduce the energy barrier of charge transfer in the Li⁺ desolvation process. Ex-situ C K-edge XANES spectra further confirm that these enriched charges of sp^x-hybridized orbitals activate pentagonal defects as high-activity adsorption sites and donate more negative charge to the solvated Li⁺ adsorbed on the surface, thus forming stronger Li–C coordinate bonds for Li⁺ desolvation in an extremely cold environment.

—Lu et al.

The authors acknowledge funding from the Fundamental Research Funds for the Central Universities (China), the National Natural Science Foundation of China, the Ministry of Science and Technology of China, the Science and Technology Project of Guangdong Province, the Chemistry and Chemical Engineering Guangdong Laboratory and Beijing Jiaotong University.

Resources

• Zongjing Lu, Jingnan Wang, Xuechun Cheng, Weiwei Xie, Zhiyi Gao, Xuejing Zhang, Yong Xu, Ding Yi, Yijun Yang, Xi Wang, and Jiannian Yao (2022) “Riemannian Surface on Carbon Anodes Enables Li-Ion Storage at −35 °C”
  ACS Central Science doi: 10.1021/acscentsci.2c00411