Researchers from the East China University of Science and Technology have improved the electrochemical performance of nickel-rich cathodes for use in lithium-ion batteries.
Nickel-rich layered cathodes have great potential for use in next-generation high-energy lithium-ion batteries due to their high energy density and competitive cost. However, these cathodes suffer from rapid capacity fading with long-term operation. To overcome this weakness, researchers from the East China University of Science and Technology have created a simple, one-step dual-modification strategy that can restrain these side reactions that occur, enhancing the cathode’s structural ability. This strategy will help meet the commercial requirements of nickel-rich cathodes for lithium-ion batteries.
The study, ‘Integrating trace Ti-doping and LiYO2-coating to stabilise Ni-rich cathodes for lithium-ion batteries,’ is published in the journal Particuology.
Improving nickel-rich cathodes to boost the energy density of lithium-ion batteries
Lithium-ion batteries with high energy density are urgently needed to meet the demand for the green energy transition. Currently, the use of lithium-ions is constrained by the limited specific capacity of their cathode material. Due to the structural and interfacial instability that occurs from long-term operation, nickel-rich layered cathodes always suffer from rapid capacity fading.
To try and solve these problems, scientists have used certain methods such as surface coating and elements doping with the cathode materials. However, single modification processes cannot solve the structural and interfacial instability at the same time. This strategy fails to prevent the cathode/electrolyte reaction, while the coating materials typically exhibit poor lithium-ion conductivity, increasing the interfacial impedance and decreasing the specific capacity.
To achieve advanced nickel-rich oxides with high specific capacity and long-cycling life, the team realised that a high-efficiency dual-modification was needed. The researchers’ work provides a simple, one-step dual-modification strategy that limits the interfacial parasitic side reactions and enhances the structural stability, while meeting the commercial requirements of nickel-rich cathodes. The co-modified cathode developed by the team exhibits superior electrochemical performance with excellent long-term cycling stability.
The team’s strategy to enhance the cathode
Using a simple one-step sintering strategy, the team synthesised the titanium-doped and lithium yttrium dioxide-coated (LiYO2) nickel-rich layered cathode. This strategy uses heat and pressure to form a solid mass of material. The developed method restrains the interfacial parasitic side reactions, and also enhances the cathode’s structural stability.
The team then analysed the crystallographic structure of their cathodes using X-ray diffraction. They researched the morphologies of the cathodes using scanning electron microscopy. The team applied transmission electron microscopy to characterise the hyperfine structure and elements distribution and used X-ray photoelectron spectra to study the surface element compositions and valence state. The results revealed that their cathode material had an improved capacity retention of 96.3% after 100 cycles and 86.8% after 500 cycles, much higher than the unmodified cathode materials.
The LiYO2 coating layer acts as a physical barrier that significantly restrains the interfacial parasitic side reactions and the dissolution of transition metal ions, enhancing the cathode-electrolyte interface stability. The robust titanium-oxygen bonds effectively stabilise the lattice oxygen as well as alleviate the lithium/nickel disorder. The new cathode has a faster lithium-ion diffusion rate, and outstanding electrochemical stability, improving the performance for use in lithium-ion batteries.
The team is developing their method for commercial-scale production
Looking to the future, the team aims to develop its strategy for large-scale production. “In the next step, we would like to apply this dual modification strategy to industrial large-scale production, taking both cathode materials with stable interface/crystal structure and excellent electrochemical performance,” said Hao Jiang, a professor at East China University of Science and Technology.
The team will also explore the consistency after amplification to ensure uniform doping and coating effect. “Moreover, the stability under extremely harsh conditions will be studied to ensure the safety of the material and facilitate its commercial application,” said Jiang.