Enhanced electrochemical performance of lithia/Li2RuO3 cathode by adding tris(trimethylsilyl)borate as electrolyte additive

Abstract

in this study, we used tris(trimethylsilyl)borate (tMSB) as an electrolyte additive and analysed its effect on the electrochemical performance of lithia-based (Lithia/Li 2 Ruo 3) cathodes. our investigation revealed that the addition of TMSB modified the interfacial reactions between a lithia-based cathode and an electrolyte composed of the carbonate solvents and the Lipf 6 salt. the decomposition of the Lipf 6 salt and the formation of Li 2 co 3 and-CO 2 was successfully reduced through the use of tMSB as an electrolyte additive. it is inferred that the protective layer derived from the tMSB suppressed the undesirable side reaction associated with the electrolyte and superoxides (oor o 0.5-) formed in the cathode structure during the charging process. this led to the reduction of superoxide loss through side reactions, which contributed to the increased available capacity of the Lithia/Li 2 Ruo 3 cathode with the addition of tMSB. the suppression of undesirable side reactions also decreased the thickness of the interfacial layer, reducing the impedance value of the cells and stabilising the cyclic performance of the lithia-based cathode. This confirmed that the addition of TMSB was an effective approach for the improvement of the electrochemical performance of cells containing lithia-based cathodes. One of the most important issues relating to lithium-ion batteries (LIBs) is the development of new cathodes with higher energy densities than commercially used LiCoO 2 , Li(Ni, Co, Mn)O 2 (NCM), and Li(Ni, Co, Al)O 2 (NCA) 1-7. Fundamentally, the capacity of most cathodes can be attributed to the cationic redox of transition metals such as Co, Ni, and Mn in the structure. Therefore, it is necessary to increase the amount of transition metals (per weight or volume) in the cathode structure to improve its energy density, which is not an easy task considering the crystal structure of transition metal oxides. However, if the redox reaction of the anions (such as oxygen ions) can contribute to the capacity of the cathode, this problem can be overcome. The anions are much lighter than general transition ions, therefore the cathodes can provide much higher capacity (per weight) and energy density compared to cases relying on only cationic redox reactions. Subsequently, cathodes based on anionic redox reactions have been attractive research topics of late. As promising new cathode materials, Li-Nb-Mn-O, Li-Mn-O, and Li-RuM -O (M = Sn, Nb) have been studied for years 8-13. These materials have shown high capacity-up to approximately 300 mA•g −1 based on anionic redox associated with oxygen as well as cationic redox related to transition metals. However, their sluggish kinetics and structural instability have resulted in an inferior rate capacity and cyclic performance compared to commercial cathodes 8-13. Lithia (Li 2 O)-based materials are also one of the new candidates for high-capacity cathodes based on anionic redox reactions 14-20. In fact, most of the new cathodes such as Li-Nb-Mn-O, Li-Mn-O, and Li-RuM -O (M = Sn, Nb)...

Interfacial reactions in lithia-based cathodes depending on the binder in the electrode and salt in the electrolyte

“…The C 1s spectrum of the PVDF electrode in Fig. S4a revealed the presence of C-C bonds (~284.5 eV) owing to carbon [39,40] , C-F 2 (~290.5 eV) and C-H 2 (~285.7 eV) bonds attributed to the PVDF binder [26] , and C-O-C (~287.1 eV) bonds related to the residual carbon impurities [41] . Further, the F 1s spectrum of the PVDF electrode exhibits a large peak related to LiF (~685.0 eV), corresponding to the reaction between lithia and PVDF binder, as well as a C-F 2 peak (~687.9 eV) owing to the binder [26] (Fig.…”

“…As alternatives to PVDF and LiPF 6 , polyacrylonitrile (PAN) and lithium bis(tri uoromethanesulfonyl)imide (LiTFSI) were selected, respectively, because they are less reactive as a binder [34][35] and salt [36][37][38] in LIBs. As a lithia-based cathode, Li 2 O/Li 2 RuO 3 nanocomposites were used owing to their high capacity and good cyclic performance [23,26] . The optimal combination of binder and salt was determined by comparing the available capacity and cycle life of the Li 2 O/Li 2 RuO 3 nanocomposites with different binders and salts with the same solvent (ethylene carbonate/dimethyl carbonate, EC/DMC, 1:1 vol%).…”

“…Research on suppressing the superoxide-related side reactions has focused on additives [26][27][28] . Several additives, such as vinylene carbonate (VC), vinylethylene carbonate (VEC), and uoroethylene carbonate (FEC), can suppress side reactions by forming an organic-based surface coating.…”

Interfacial reactions in lithia-based cathodes depending on the binder in the electrode and salt in the electrolyte

“…Research on suppressing the superoxide-related side reactions has focused on additives 26 – 28 . Several additives, such as vinylene carbonate (VC), vinylethylene carbonate (VEC), and fluoroethylene carbonate (FEC), can suppress side reactions by forming an organic-based surface coating.…”

“…As alternatives to PVDF and LiPF 6 , polyacrylonitrile (PAN) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were selected, respectively, because they are less reactive as a binder 34 , 35 and salt 36 – 38 in LIBs. As a lithia-based cathode, Li 2 O/Li 2 RuO 3 nanocomposites were used owing to their high capacity and good cyclic performance 23 , 26 . The optimal combination of binder and salt was determined by comparing the available capacity and cycle life of the Li 2 O/Li 2 RuO 3 nanocomposites with different binders and salts with the same solvent (ethylene carbonate/dimethyl carbonate, EC/DMC, 1:1 vol%).…”