title: Aligned Li+Tunnels in Core-Shell Li(NixMnyCoz)O2@LiFePO4Enhances Its High Voltage Cycling Stability as Li-ion Battery Cathode.
abstract: Layered transition-metal oxides (Li[NixMnyCoz]O2, NMC, or NMCxyz) due to their poor stability when cycled at a high operating voltage (>4.5 V) have limited their practical applications in industry. Earlier researches have identified Mn(II)-dissolution and some parasitic reactions between NMC surface and electrolyte, especially when NMC is charged to a high potential, as primarily factors responsible for the fading. In our previous work, we have achieved a capacity of NMC active material close to theoretical value and optimized its cycling performance by a depolarized carbon nanotubes (CNTs) network and an unique "pre-lithiation process" that generates an in situ organic coating (∼40 nm) to prevent Mn(II) dissolution and minimize the parasitic reactions. Unfortunately, this organic coating is not durable enough during a long-term cycling when the cathode operates at a high potential (>4.5 V). This work attempts to improve the surface protection of the NMC532 particles by applying an active inorganic coating consisting of nanosized- and crystal-orientated LiFePO4(LFP) (about 50 nm, exposed (010) face) to generate a core-shell nanostructure of Li(NixMnyCoz)O2@LiFePO4. Transmission electron microscopy (TEM) and etching X-ray photoelectron spectroscopy have confirmed an intimate contact coating (about 50 nm) between the original structure of NMC and LFP single-particle with atomic interdiffusion at the core-shell interface, and an array of interconnected aligned Li+tunnels are observed at the interface by cross-sectional high-resolution TEM, which were formed by ball-milling and then strictly controlling the temperature below 100 °C. Batteries based on this modified NMC cathode material show a high reversible capacity when cycled between 3.0 and 4.6 V during a long-term cycling.
authors: School of Advanced Materials, Peking University Shenzhen Graduate School , Shenzhen 518055, China.
authors: Zhongzhen
authors: Z
authors: Wu
authors: School of Advanced Materials, Peking University Shenzhen Graduate School , Shenzhen 518055, China.
authors: Shunping
authors: S
authors: Ji
authors: School of Advanced Materials, Peking University Shenzhen Graduate School , Shenzhen 518055, China.
authors: Tongchao
authors: T
authors: Liu
authors: School of Advanced Materials, Peking University Shenzhen Graduate School , Shenzhen 518055, China.
authors: Yandong
authors: Y
authors: Duan
authors: School of Advanced Materials, Peking University Shenzhen Graduate School , Shenzhen 518055, China.
authors: Shu
authors: S
authors: Xiao
authors: School of Advanced Materials, Peking University Shenzhen Graduate School , Shenzhen 518055, China.
authors: Yuan
authors: Y
authors: Lin
authors: U.S. Army Research Laboratory , Adelphi, Maryland 20783, United States.
authors: Kang
authors: K
authors: Xu
authors: School of Advanced Materials, Peking University Shenzhen Graduate School , Shenzhen 518055, China.
authors: Feng
authors: F
authors: Pan
keywords: Li(Ni0.5Mn0.3Co0.2)O2; aligned Li+ tunnels; core−shell coating; nano-LiFePO4