Significance Statement
Lithium-ion batteries, one of energy storage device for electric vehicles are considered to be the most promising storage device due to their large capacity, excellent rate capability and low cost. They however pose safety concerns due to their rapid temperature rise or even combustion of the batteries.
Researchers from AR-3, Samsung R&D Institute Japan and Energy Lab, SAIT, Samsung Electronics Co. in Republic of Korea proposed a new type of coating, diamond-like carbon to reduce the interface resistivity in sulfide-based all-solid state lithium-ion batteries. Their study published in Journal of Power Sources, investigated the effects of diamond-like carbon coating layer on battery’s electrochemical performance and its positive impact was clarified.
All solid-state lithium-ion batteries have been used widely due to their non-volatile inorganic solids loading to highly conductive materials with lithium-ion conductivities in range of 10-3-10-2 Scm-1. However, high interfacial resistance due to reactions between the sulfide solid electrolyte and active materials affects the performance of all solid-state lithium-ion batteries . In order to curb this, several buffer layers have been proposed to suppress the formation of a high-resistance layer. These buffer layers though, successfully prevents direct contact between solid electrolyte and active materials, they are generally poor in conduction of lithium ions as they hinder the migration of lithium ions at the interface of sulfur-based solid electrolyte and oxide cathode materials.
The proposed diamond-like carbon by Visbal et al. (2016) is known for its uniqueness in physicochemical properties. Diamond-like carbon offers various advantages in terms of hardness, chemical inertness, electrolyte-resistant and compatibility layer with lithium anodes.
For this experiment LiNi0.8Co0.15Al0.05O2 (NCA) was used as cathode active material. Diamond-like carbon coated NCA was prepared using penning ionization gauge based chemical vapor deposition equipment. Effect of plasma pretreatment during the chemical vapor deposition process was also determined. The crystallinities and impurities of samples were examined by X-ray diffracted patterns using Empyrean X-ray diffraction (XRD) system diffractometer. Morphology and microstructure of the diamond-like carbon layer were characterized using a Transmission Electron Microscopy with Energy Dispersion X-ray analysis while Electron Energy-Loss Spectroscopy (EELS) spectra were taken to characterize the nature of diamond-like carbon coating.
Effect of the diamond-like carbon coating on the performance of sulfide-based all solid-state lithium-ion batteries were investigated using electrochemical cells of amorphous Li2-P2S5 (75:25mol%) electrolyte, cathode composite prepared by mixing Vapor grown Carbon Fiber (VCF) and Li2-P2S5 (75:25mol%) in weight ratio of 60:5:35 respectively. Anode composite was similarly fabricated by mixing artificial graphite with Vapor grown Carbon Fiber (VCF) and Li2-P2S5 (75:25mol%) in weight ratio 60:5:35. Electrochemical behavior of the all solid-state lithium-ion batteries were investigated by galvanostatic charge-discharge cycle and Electrochemical Impedance Spectroscopy (EIS).
Results from the XRD patterns showed that both diamond-like carbon coated and bare NCA samples were single phased and isostructural with LiNiO2 giving no obvious difference between the two X-ray diffraction spectra. This result indicates that diamond-like carbon coating does not alter crystal structure and lattice constants of NCA.
Mean thickness from Transmission Electron Microscopy image of cross-sectional area of diamond-like carbon coated NCA particle was computed to be 4.3nm. Energy-dispersive X-ray spectroscopy analysis showed the sp2 bonding ration of diamond-like carbon coated NCA powder was estimated to be around 55% from C K-edge peak as expected for a diamond-like carbon coating.
Specific capacities of bare, plasma coated and diamond-like carbon coated were 119.9, 114.9 and 120.7mAhg-1 with initial columbic efficiency of 66.6, 64.9 and 66.5% respectively. Measured impedance of resistance obtained at cell kinetics of both cathode and anode charge transfer for bare, plasma coated NCA and diamond-like coated NCA were 234, 177 and 70Ώ respectively.
Cycle performance of the three cells with different positive electrode materials was compared. The bare and plasma coated NCA cells exhibited the drop to 70% and 75% of their initial capacity after 100cycles while the diamond-like carbon coated NCA cell showed higher capacity retention, retaining 91% after 100 cycles.
Further experiment results showed that diamond-like carbon coating minimizes the formation of fragment species at the surface was the lowest for the sample. These results proved that diamond-like carbon coating prevents S– and P– ions of solid electrolyte to react with oxygen of cathode active particles which leads to interfacial resistance and deterioration of electrochemical property.
Based on this analysis, Visbal et al. (2016) fabrication of diamond-like carbon coating of NCA cells prevents slide reaction between the cathode and sulfide electrode and improvement of electrochemical properties of the cell was achieved.
Journal Reference
Heidy Visbal1,Yuichi Aihara1 , Seitaro Ito1, Taku Watanabe1,Youngsin Park2, Seokgwang Doo2. The effect of diamond-like carbon coating on LiNi0.08Co0.15Al0.05O2 particles for all solid-state lithium-ion batteries based on Li2S-P2S5 glass-ceramics. Journal of Power Sources, 2016, Volume 314, pp 85-92.
Show Affiliations- AR-3, Samsung R&D Institute Japan, Minoh Semba Center Bldg., 2-1-11 Semba Nishi, Minoh-shi, Osaka 562-0036, Japan
- Energy Lab, SAIT, Samsung Electronics Co., Ltd., San 14-1, Nongseo-Dong, Giheung-Gu, Yongin-Si, Gyeonggi-Do 446-712, Republic of Korea
Go To Journal of Power Sources,
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