Fast-charging capability of lithium-ion batteries (LIBs) is a critical parameter that affects their application in 3C electronics and electric vehicles. The structure of electrode plays a important role in determining the fast-charging capability of batteries. A general approach to enhance the fast-charging performance of LIBs is reducing the the mass loading and thickness of the electrodes, which shorten the ion and electronic transport distance. However, such an operation significantly sacrifices the overall energy density of the batteries. Thus, it is highly desirable to achieve fast charging of electrodeswith high areal capacity, which is of key importance in realizing high-energy-density LIBs with fast-charging capability.
Professor Yongming Sun’ group proposed a single-layer chunky particle electrode architecture with vertically aligned charge transport pathways, which could solve the problem of slow charge transport in highly loaded particle electrodes (Figure 1). As a demonstration, a single-layer-particle electrode, where red phosphorus (red P) was embedded in the vertically aligned nanochannels (~ 22 nm) of chunky graphene assemblies (red P/VAG, ~60 μm) was reported. Such an electrode displayed a high areal capacity of 5.6 mAh cm-2, and its specific capacity and fast-charging performance far exceed those of commercial graphite or lithium titanate anodes. When coupled with commercial LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode, a pouch cell showed stable cycling with high energy density (405 Wh kg-1), and fast-charging performance (10 min, 204 Wh kg-1). This electrode architecture could simultaneously achieve fast charging and high energy density of LIBs, thus guiding the design of high-performance material and electrode structures.
Figure 1. Schematic illustration of regular particle electrode consisting of randomly stacked active particles with high tortuosity and single-layer chunky particle electrode with low-tortuosity inner nanochannels for ion transport and conductive pathway for electron transfer.Active particles with random charge transport orientations are randomly stacked in traditional electrodes, which leads to high tortuosity and inner particle/electrode resistance.Vertical inner nanochannels enable fast ion transport and conducting pathways accelerate electron transport in single-layer chunky particle electrode.
Figure 2. (a) Schematic illustration of the fabrication of red P/VAG composite. (b and c) SEM (b) and TEM (c) images of VAG. (d) Dark-field STEM and corresponding elemental mapping images of red P/VAG composite. (e) Nitrogen adsorption/desorption isotherms of VAG and red P/VAG composite. (f and g) Cross-section SEM images of single-layer red P/VAG particle electrode. The inset in (e) showed pore size distribution plots of VAG and red P/VAG composite.
Figure 3. (a) The pouch cell configuration using single-layer red P/VAG particle electrode. (b and c) Rate capability (b) and charge/discharge profiles (c) of NCM622||single-layer red P/VAG pouch cell at various charging current densities from 1 to 40 mA cm-2. The discharge current density was fixed as 0.5 mA cm-2. (d) Eg and Ev achieved within the charging times of 30, 20, 15, 12, 10 and 8 min. (e) Ragone (double logarithmic) plots of energy density and power density for electrochemical energy storage devices and NCM622||single-layer red P/VAG full cell based on the pouch cell data. (f) The cycling performance of NCM622||single-layer red P/VAG pouch cell at the high charging current density of 15 mA cm-2(corresponding to the charge time of 20 minutes) and (g) charge/discharge profiles for different cycles. The pouch cell was activated at 0.5 mA cm-2 for three cycles.
Related work has been published on Advanced Materials (https://onlinelibrary.wiley.com/doi/10.1002/adma.202202892), with the title Single-Layer-Particle Electrode Design for Practical Fast-Charging Lithium-ion Batteries on May 31, 2022. The first unit for this research is the Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, and it has been funded by the National Natural Science Foundation of China.
