A Single‐Pot Co‐Precipitation Synthesis Route for Ni‐Rich Layered Oxide Materials with High Cycling Stability

Abstract

In this work we report variations of LiNi 0.88 Mn 0.06 Co 0.06 O 2 synthesised through a single-pot oxalic acid co-precipitation route, in which all cation precursors were added in the same step. The effects of Al-doping, heat-treatment temperature and Li precursor excess were investigated with physicochemical and electrochemical characterisation. Phase pure and well-ordered polycrystalline materials were successfully synthesised for all Aldoped and undoped compositions. Undoped LiNi 0.88 Mn 0.06 Co 0.06 O 2 prepared at 750 °C with 4 at% excess Li precursor showed excellent cycling stability in NMC j j LTO cells with an initial capacity of 201 mAh/g at 0.1 C at 20 °C, and a capacity retention of 81 % after 415 cycles. The Al-doped variations LiNi 0.88 Mn 0.04 Co 0.06 Al 0.02 O 2 and LiNi 0.88 Mn 0.06 Co 0.04 Al 0.02 O 2 were synthesised, and they showed similar initial electrochemical performance to undoped LiNi 0.88 Mn 0.06 Co 0.06 O 2 , but Aldoping via the oxalic acid co-precipitation route resulted in shorter cycle life. The study outlines the importance of the processing parameters to achieve Ni-rich layered oxides with a long cycle life without further surface modifications.

Interphase Engineering of LiNi0.88Mn0.06Co0.06O2 Cathodes Using Octadecyl Phosphonic Acid Coupling Agents

“…Ni-rich layered oxide LiNi 0.88 Mn 0.06 Co 0.06 O 2 (NMC) was synthesized through a single-pot oxalic acid coprecipitation route developed in earlier work . In brief, LiNO 3 (99%, Alfa Aesar), Ni­(CH 3 COO) 2 *4H 2 O (≥98%, Alfa Aesar), Mn­(CH 3 COO) 2 *4H 2 O (≥99%, Merck), and Co­(CH 3 COO) 2 *4H 2 O (≥98%, Sigma-Aldrich) were used as precursors.…”

“…Measurements were recorded on a Bruker D8 A25 DaVinci X-ray diffractometer with Mo–K α radiation (λ = 0.71 Å), using a focusing Göbel mirror and equipped with a LynxEye XE 1D detector. The structural analyses via Rietveld refinements were similar as described in ref . In short, the refinements were based on an α-NaFeO 2 structure with an R 3̅ m space group with Li in the 3a position, M (Ni, Mn, Co) in the 3b position, and O in the 6c position.…”

“…In this work, in-house synthesized LiNi 0.88 Mn 0.06 Co 0.06 O 2 (NMC) developed in our earlier work is coated using octadecyl phosphonic acid (OPA) as a coupling agent through a wet-chemical route. The OPA molecule (Figure S1) has a –PO­(OH) 2 functional group at the end of a linear hydrocarbon chain, with the added benefits of a hydrophobic tail and a functional group with a strong affinity to oxygen as P–O bonds are considered strong .…”