Elucidating the Effect of Borate Additive in High‐Voltage Electrolyte for Li‐Rich Layered Oxide Materials

Abstract

high energy density LIBs is increasing. [2] Lithium-rich layered oxide (LRLO) as a high-energy cathode material has attracted many interests due to its large specific capacity (over 300 mAh g −1 ). [3,4] Accompanied by Li extraction/insertion during charge and discharge, LRLO experiences not only the transition metal (TM) redox but also the oxygen redox which contributes a large portion to its high capacity. [5,6] Despite its high capacity, the practical deployment of LRLO is hindered by voltage fade and capacity decay during electrochemical cycling. [7,8] These two issues are correlated to the activation of oxygen redox at high voltage (>4.5 V versus Li + /Li 0 ), which leads to surface and structure degradation during cycling, such as the formation of oxygen vacancies and irreversible oxygen loss, [8,9] the migration and the dissolution of TM, [10,11] the formation of spinel-like phase, [4] and the accumulation of microstrain. [12] Intensive materials modification efforts have been devoted to addressing the capacity and voltage decay issues in LRLO. Surface coating with oxides or fluorides such as Al 2 O 3 and AlF 3 was applied to reduce the oxygen release and protect the surface from acidic species in the electrolyte. [13][14][15] Both cation and anion doping such as Mg, Mo, F were also designed to mitigate the capacity and voltage decay through the altering of electronic structure and the suppression of structural degradation. [16][17][18] Heat treatment and re-lithiation on cycled LRLO materials were also studied to recover the capacity and voltage decay after electrochemical cycling through the recovery of the honeycomb ordering in the TM layer. [19,20] Besides the modification on active materials, many cell components have also been optimized for high-voltage operation such as the binder and conductive agents. [21] However, the compatibility of the electrolyte with the charged state of LRLO is often neglected in the literature. The activation step ubiquitously seen in anionic redox materials occurs at 4.5 V versus Li + / Li 0 . For the commonly used carbonate-based liquid electrolytes, when the voltage is pushed above this limit (4.5 V), the electrolytes decompose through the following processes: carbonatebased organic solvents such as ethylene carbonate (EC) oxidize and decompose at high voltage, accompanied by dehydrogenation reaction as the protons attached to the carbon in the carbonate solvents are dissociated. [22] The protons may further Lithium-rich layered oxides (LRLO) have attracted great interest for high-energyLi-ion batteries due to their high theoretical capacity. However, capacity decay and voltage fade during the cycling impede the practical application of LRLO. Herein, the use of lithium bis-(oxalate)borate (LiBOB) as an electrolyte additive is reported to improve the cycling stability in high voltage LRLO/graphite full cells. The cell with LiBOB-containing electrolyte delivers 248 mAh g −1 initial capacity and shows no capacity decay after 70 cycles as well as 95.5% retention after 150 c...

Mo2C catalyzed low-voltage prelithiation using nano-Li2C2O4 for high-energy lithium-ion batteries

“…The F 1s spectra (Fig. 7f) show that the peaks at 689.2, 687.4, 686.7, and 684.3 eV belong to C-F, P-F, P-O-F, and LiF species, respectively [38]. The increase in inorganic LiF on the SiO surface after NLM addition possibly ensures a superior and stable SEI formation, thus enabling the LCO-NLM/SiO full cell to exhibit good cycling stability.…”

Advances in studying interfacial reactions in rechargeable batteries by photoelectron spectroscopy

“…Such compounds added to the electrolyte, typically in concentrations of <10 %, are often designed to improve interfacial chemistry. [109][110][111][112][113] The role of tris(trimethylsilyl) phosphite (TMSPi) as an electrolyte additive to improve the electrochemical performance of NMC811/Si-Graphite cells was investigated by synchrotron-based XPS depth profiling. 114 The morphological and compositional differences of the CEI and SEI were probed for the cathode and anode, respectively.…”

“…Such compounds added to the electrolyte, typically in concentrations of <10%, are often designed to improve interfacial chemistry. 109–113…”

Critical Review on cathode–electrolyte Interphase Toward High-Voltage Cathodes for Li-Ion Batteries

“…A mechanism study for the LiBOB-enabled 4.5 V lithium-rich layered oxides||graphite full cells was further conducted (Fig. 5 b), confirming the formation of a uniform interphase with B-F species on high-voltage cathodes under cryo-condition [ 88 ]. In situ formation of F- and B-rich CEI layer on LiNiO 2 cathode was demonstrated using LiDFOB as an additive, maintaining high capacity retention of > 80% (400 cycles) at a high cutoff voltage of 4.4 V [ 89 ].…”

“…b Schematic of enhanced full cell performance for LiBOB additive electrolyte in high-voltage system. Copyright from Ref [88].…”