Synergetic Effect of Electrolyte Coadditives for a High-Voltage LiCoO₂Cathode

Abstract

Currently widely used carbonate-based electrolytes face difficulty in ensuring that the lithium-ion batteries work beyond 4.2 V for the purpose of energy density improvement. Herein, we report a novel electrolyte that emphasizes the synergistic effect of fluoroethylene carbonate (FEC) and 2-(trifluoromethyl) phenyl boric acid (2-TP) as coadditives, enabling the LiCoO 2 cathode to operate stably under high voltages. With the addition of 1% 2-TP and 10% FEC into a carbonate-based electrolyte, LiCoO 2 shows a significantly improved cyclic stability. Spectral characterizations, electrochemical measurements, and theoretical calculations demonstrate that the improved cyclic stability can be attributed to the cathode−electrolyte interphase (CEI) derived from FEC and 2-TP. These two additives are preferentially oxidized on the LiCoO 2 electrode into their oxidation decomposition products to construct a robust and lowimpedance CEI with inorganic LiF uniformly dispersed in the organic B-containing matrix. This unique CEI construction provides a facile solution to the challenges in developing high-energy-density lithium-ion batteries based on high-voltage cathodes, not limited to LiCoO 2 .

Pushing Lithium Cobalt Oxides to 4.7 V by Lattice‐Matched Interfacial Engineering

“…According to previous reports, the evolution of the (003) peak is closely related to the structural change of LCO and the shift of peak position can reflect the volume variation of crystal cell. [ 23 ] As shown in Figure 3d–i, the structural evolution of bare LCO and LCPO–LCO is similar at the voltage range of 3.0–4.55 V. The distinct difference in structural transition appears above 4.55 V. For the bare LCO sample, the phase transition from O3 to H1‐3 is initiated at 4.55 V (Figure 3e), and the ratio of H1‐3 to O3 progressively evolves from 8.61% to 28.29% as more Li ions are removed from the lattice. The high proportion of the H1‐3 phase means more severe slippage of the O–Co–O slabs, accompanied by the lithium rearrangement and large volume shrinkage.…”

Highly Stable 4.6 V LiCoO2 Cathodes for Rechargeable Li Batteries by Rubidium‐Based Surface Modifications

“…Moreover, the high charging potentials induce formation of resistive surface layers (due to irreversible surface phase changes or formation of resistive passivation films), which increase cells' impedance and cause rapid degradation. [ 6,7 ]…”

“…Moreover, the high charging potentials induce formation of resistive surface layers (due to irreversible surface phase changes or formation of resistive passivation films), which increase cells' impedance and cause rapid degradation. [6,7] In light of this situation, significant efforts were made to stabilize the electrodes-electrolyte solutions interfaces by application of various coating chemistries. As shown in several recent studies, implementation of surface layers such as Li-Al-F, [8,9] AlZnO, [10] or AlPO 4 @Li 3 PO 4 [11] significantly enhanced 4.6 V cathodes stability.…”

Insight into the Improved Performances of Ni-Rich/Graphite Cells by 1,3,5-Trimethyl-1,3,5-tris(3,3,3-trifluoropropyl) Cyclotrisiloxane as an Electrolyte Additive

“…Comparatively, in situ constructing interphases on cathodes by optimizing the formula of an electrolyte is valid, especially applying electrolyte additives that can be used in far less amount than solvents and salts. − The interphases are usually constructed from the products of the additives through oxidation decomposition, and therefore, the as-constructed interphases can uniformly cover the active cathode materials and effectively avoid the direct contact between cathode materials with electrolytes. Many electrolyte additives have been widely used in commercialized LIBs, but few are available for high-voltage Ni-rich cathodes. − …”