Lithium bis(oxalate)borate, LiB(C 2 O 4 ) 2 (LiBOB), is one of the most important electrolyte additives for Li-ion batteries (LIBs) due to its numerous advantages such as thermal stability, good solubility in organic solvents, high conductivity, and low cost as well as providing safer operations with superior electrochemical performance compared to conventional electrolyte combinations. However, the use of LiBOB is limited due to slight instability issues under ambient conditions that might require extra purification steps and might result in poorer performances in real systems. Here, we address some of these issues and report the high purity water free LiBOB synthesized with fewer processing steps employing lithium carbonate, oxalic acid, and boric acid as lowcost starting materials, and via ceramic processing methods under protective atmosphere. The physical and chemical characterizations of both anhydrous and monohydrate phases are performed with X-ray powder diffraction (XRPD), Fourier-transform infra-red spectroscopy (FTIR), Raman spectroscopy and scanning electron microscopy (SEM) analyses to determine the degree of the purity and the formation of impurities like LiBOB.H 2 O, HBO 2 and Li 2 C 2 O 4 as a result of the aging investigations performed. Differential thermal analysis (DTA) is applied to determine the optimum synthesis conditions for anhydrous LiBOB and to analyze the water loss and the decomposition of LiBOB.H 2 O. Aging experiments with the water free LiBOB are carried out to evaluate the effect of humidity in the phase changes and resulting impurities under various conditions. The detrimental effect of even slightest humidity conditions is shown, and protective measures during and after the synthesis of LiBOB are discussed. Anhydrous LiBOB could be widely used as an electrolyte additive to improve the overall electrochemical performances for LIBs through development of a protective solid electrolyte interphase (SEI) on the surface of high voltage cathodes and bringing about superior electrochemical properties with increased cycling stability, rate capability and coulombic efficiency, if synthesized, purified, and handled properly before use in real electrochemical systems.
Lithium bis(oxalate) borate, LiB(C 2 O 4 ) 2 (LiBOB) can be used as an electrolyte additive for lithium-ion batteries (LIBs) to prevent structural change and electrolyte decomposition by developing a protective solid electrolyte interphase (SEI) on the cathode surface. However, impurities present in LiBOB result in significant electrochemical performance decays related to higher full cell impedance. Here, a practical purification technique is performed to remove these impurities within the as-synthesized anhydrous LiBOB in which we further add 1 wt % in 1 M LiPF 6 in EC:DMC (1:1) electrolytes to achieve a more stable cycling performance for high voltage applications of LiCoO 2 (LCO) cathodes. The phase and purity of as-synthesized LiBOB and recrystallized LiBOB is determined by a combination of X-ray powder diffraction (XRPD), Fourier-transform infrared (FTIR) spectra, and scanning electron microscopy (SEM) measurements. The LIB performance with the addition of high purity LiBOB as an electrolyte additive is investigated via galvanostatic charge−discharge cycling, rate capability, and cyclic voltammetry (CV) measurements within a voltage range of 3.0−4.4 V. The cell containing 1 wt % recrystallized LiBOB shows superior cycling performance, rate capability with higher energy density, and Coulombic efficiency in comparison with the reference cell through the formation of a passivation layer on the LCO surface. Thus, for the LiBOB added cell, the crystal structure of LiCoO 2 is well-maintained even at higher potentials after 100 cycles according to the ex situ XRPD and SEM analyses. Therefore, high-purity LiBOB improves the interfacial stability of the LCO cathode by inhibiting oxidative decomposition of electrolytes, undesirable structural changes, and cobalt dissolution bringing about safer cycling even at high operation voltages.
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