title: Olivine-type nanosheets for lithium ion battery cathodes.
abstract: Olivine-type LiMPO4 (M = Fe, Mn, Co, Ni) has become of great interest as cathodes for next-generation high-power lithium-ion batteries. Nevertheless, this family of compounds suffers from poor electronic conductivities and sluggish lithium diffusion in the [010] direction. Here, we develop a liquid-phase exfoliation approach combined with a solvothermal lithiation process in high-pressure high-temperature (HPHT) supercritical fluids for the fabrication of ultrathin LiMPO4 nanosheets (thickness: 3.7-4.6 nm) with exposed (010) surface facets. Importantly, the HPHT solvothermal lithiation could produce monodisperse nanosheets while the traditional high-temperature calcination, which is necessary for cathode materials based on high-quality crystals, leads the formation of large grains and aggregation of the nanosheets. The as-synthesized nanosheets have features of high contact area with the electrolyte and fast lithium transport (time diffusion constant in at the microsecond level). The estimated diffusion time for Li(+) to diffuse over a [010]-thickness of <5 nm (L) was calculated to be less than 25, 2.5, and 250 μs for LiFePO4, LiMnPO4, and LiCoPO4 nanosheets, respectively, via the equation of t = L(2)/D. These values are about 5 orders of magnitude lower than the corresponding bulk materials. This results in high energy densities and excellent rate capabilities (e.g., 18 kW kg(-1) and 90 Wh kg(-1) at a 80 C rate for LiFePO4 nanosheets).
authors.affiliation: School of Materials Science and Engineering, Nanyang Technological University, 639798, Singapore.
authors.forename: Xianhong
authors.initials: X
authors.lastname: Rui
authors.forename: Xiaoxu
authors.initials: X
authors.lastname: Zhao
authors.forename: Ziyang
authors.initials: Z
authors.lastname: Lu
authors.forename: Huiteng
authors.initials: H
authors.lastname: Tan
authors.forename: Daohao
authors.initials: D
authors.lastname: Sim
authors.forename: Huey Hoon
authors.initials: HH
authors.lastname: Hng
authors.forename: Rachid
authors.initials: R
authors.lastname: Yazami
authors.forename: Tuti Mariana
authors.initials: TM
authors.lastname: Lim
authors.forename: Qingyu
authors.initials: Q
authors.lastname: Yan