Trimethyl Borate as Film-Forming Electrolyte Additive To Improve High-Voltage Performances

Abstract

Enhancing the stability of the interface between the electrode and electrolyte at high voltages is crucial concerning the development of Li-ion batteries with high energy densities. Application of some additives in the electrolyte is not only the simplest but also the most effective way to form a protection layer against the electrolyte decomposition and the electrolyte corrosion to the electrode. Herein, we introduce trimethyl borate (TMB) as an additive of the commercial electrolyte to ameliorate the performance of a LiCoO2 cell charged to 4.5 V because its addition lowers the oxidation potential of the baseline electrolyte (3.75 V vs 4.25 V). By being oxidized preferentially and thus forming a compact protection layer of about 25 nm thick on the cathode surface, the additive suppresses the electrolyte decomposition and protects the LiCoO2 cathode against the structural degradation. The capacity retention of the cell after 100 cycles between 2.5 and 4.5 V at 0.1 C increases from 64 to 81% when 2.0 wt % TMB is added into the baseline electrolyte. The X-ray photoelectron spectroscopic results demonstrate the oxidation of TMB on the cathode and therefore the suppressed decomposition of the electrolyte. The results of the X-ray diffraction and Raman spectroscopy show the better structural maintenance of the LiCoO2 material in the TMB-containing electrolyte. The protection mechanism of the TMB additive was comprehensively studied.

Dual‐Carbon Lithium‐Ion Capacitors: Principle, Materials, and Technologies

“…According to the mechanism of the SEI formation, these compounds can be roughly classified as vinyl additives and reactive additives [44] . The former includes, but is not limited to, vinyl carbonate and vinyl ethylene carbonate, [44] and the latter includes, but is not limited to, fluoroethylene carbonate, [45] fluorosulfonyl isocyanate, [46] sulfates and sultones, [47] phosphates and phosphites, [47b,48] and borates, [47b,49] as well as Li salts such as lithium bis(fluorosulfonyl)imide (LiFSI), [50] lithium bis(oxalato)borate (LiBOB), [51] lithium difluoro(oxalato)borate (LiDFOB), [52] and LiPO 2 F 2 [53] . On the other hand, using a hybrid of a Li salt and another Li or other cationic salts would be an option for improving the capacity retention of the LICs since the cations have a great effect on the reversibility and stability of the oxygen functional groups in the ACs [33] …”

Challenges and Strategies for Fast Charge of Li‐Ion Batteries

“…For the layered cathode, most of the improvements by using electrolyte additives are based on reactions with the surficial Li residual compounds (such as Li 2 CO 3 , LiOH, and Li 2 O) to reconstitute a more conductive or more favorable CEI . Therefore, effective additives for the layered cathode are mainly centered on the compounds that can react with the alkaline Li residual compounds, such as sulfates & sultones, phosphates & phosphites, and borates . As pointed out in Section 3.1, electrolyte solvents are subject to electrochemical reduction on the graphite anode under fast charge .…”

Design aspects of electrolytes for fast charge of Li‐ion batteries

“…52 54,55 phosphates & phosphites, 55,56 and borates. 55,57 For these types of additives, they can be alternatively applied to the cathode-coating process, rather than adding them into the electrolyte. Furthermore, the electrode-coating process (ie, vigorously stirring in the mixing process and heating during removing solvent and drying processes) can make the reaction more thorough.…”

“…Some electrolyte additives are based on chemical reactions with alkaline Li residual compounds (mainly Li 2 CO 3 , LiOH, and Li 2 O) on the surface of layered cathode materials, especially those with high Ni content, to reconstitute a more conductive and robust CEI 53 . Such additives include, but are not limited to, sulfates & sultones, 54,55 phosphates & phosphites, 55,56 and borates 55,57 . For these types of additives, they can be alternatively applied to the cathode‐coating process, rather than adding them into the electrolyte.…”