Highly Enforced Rate Capability of a Graphite Anode via Interphase Chemistry Tailoring Based on an Electrolyte Additive

Abstract

The rate capability of lithium-ion batteries is highly dependent on the interphase chemistry of graphite anodes. Herein, we demonstrate an anode interphase tailoring based on a novel electrolyte additive, lithium dodecyl sulfate (LiDS), which greatly improves the rate capability and cyclic stability of graphite anodes. Upon application of 1% LiDS in a base electrolyte, the discharge capacity at 2 C is improved from 102 to 240 mAh g −1 and its capacity retention is enhanced from 51% to 94% after 200 cycles at 0.5 C. These excellent performances are attributed to the preferential absorption of LiDS and the as-constructed interphase chemistry that is mainly composed of organic long-chain polyether and inorganic lithium sulfite. The long-chain polyether possesses flexibility endowing the interphase with robustness, while its combination with inorganic lithium sulfite accelerates lithium intercalation/deintercalation kinetics via decreasing the resistance for charge transfer.

Formation Mechanism and Regulation of LiF in a Solid Electrolyte Interphase on Graphite Anodes in Carbonate Electrolytes

“…As the constant potential changes from 1.3 to 0.7 V, the LiF peak intensity increases, indicating that more LiF can be formed on the graphite surface by applying a more negative potential. On the fresh electrode, the species C–C at 284.8 eV, C–H at 286.4 eV, and C–F at 291.1 eV in the C 1s spectrum , (Figure S5a) and −CO at 532.5 eV and −C–O at 533.6 eV O 1s spectra (Figure S5b) can be identified, which come from graphite, conductive acetylene black, and PVDF binder. The O-containing species can be ascribed to the minor oxygen in graphite and acetylene black.…”

“…7,14−16 Among these components, LiF has high mechanical strength, low solubility, and a wide band gap, ensuring the SEIs with sufficient chemical and mechanical stability to prevent graphite from structural destruction and suppress the further reduction decomposition of the base electrolytes. 17,18 On the other hand, crystal LiF as nanoparticles is dispersed in organic texture, resulting in abundant inorganic/organic interfaces that are beneficial for Li + transportation and ensure the SEIs with ionic conductivity. 19−24 Since LiF plays a very important role in the stability of SEIs on graphite anodes, LiF-rich SEIs were designed by introducing F-containing compounds as solvents or electrolyte additives, the most representative of which is fluoroethylene carbonate (FEC).…”

“…It has been known that the SEIs on graphite anodes without using any additives are derived from the reduction decomposition of the base electrolytes, ,− which consist of inorganic compounds, such as Li 2 CO 3 , Li 2 O, and LiF, and organic ones, such as lithium ethylene dicarbonate ((CH 2 COCO 2 ) 2 Li 2 , LEDC), lithium methyl carbonate (CH 3 OCO 2 Li, LMC), and lithium ethyl carbonate (LEC, CH 3 CH 2 OCO 2 Li). ,− Among these components, LiF has high mechanical strength, low solubility, and a wide band gap, ensuring the SEIs with sufficient chemical and mechanical stability to prevent graphite from structural destruction and suppress the further reduction decomposition of the base electrolytes. , On the other hand, crystal LiF as nanoparticles is dispersed in organic texture, resulting in abundant inorganic/organic interfaces that are beneficial for Li + transportation and ensure the SEIs with ionic conductivity. − …”

Quantum Chemical Characteristics of Additives That Enable the Use of Propylene Carbonate-Based Electrolytes

“…SEIs composed of these components have a dense and stable interface that prevents degradation and capacity loss [83]. The Li 2 SO 3 as component of the anodeelectrolyte interphase is believed to be beneficial for ionic conductivity [84]. Of course, alkyl sulfide is a component of SEI on the surface of graphite anodes [85], but we draw attention here to the finding that the additives enable PC-based electrolytes have molecular characteristics that favor the reaction pathway (path A) that commonly forms inorganic materials, such as Li 2 CO 3 and Li 2 SO 3 .…”

Insight into the Contribution of Nitriles as Electrolyte Additives to the Improved Performances of the LiCoO2 Cathode

“…Lithium-ion batteries (LIBs) have been widely used in a variety of areas because their performances outperform other rechargeable batteries. − Although it has been over 3 decades since LIBs were first commercialized, lithium cobalt oxide (LiCoO 2 ) is dominating as the cathode of LIBs as a result of the high volumetric specific energy, especially for powering portable electronic devices. − It will still attract much attention in the future because of its potential to improve the energy density of LIBs via enhancing working voltages. The big challenge for the application of LiCoO 2 under high voltages is the interfacial instability of LiCoO 2 /electrolytes, where parasitic reactions take place. − Under high voltages that are beyond their electrochemically stable windows, electrolyte components, solvents, and salts will be oxidized on the cathode, yielding detrimental species, including gases that inflate batteries, deposits that add interfacial impedance for lithiation/delithiation, and dissolvable species, such as hydrogen fluoride (HF), that might corrode active materials and current collectors. − The corroding is accompanied by the dissolution of transition metal ions from cathodes, which might transport to and deposit on anodes and catalyze the reduction decomposition of the electrolyte components.…”