Trimethylsilyl Borate Research Articles

Design and Reaction Mechanism of Rechargeable Lithium-Carbon Fluoride Battery.

Recharging primary batteries is of great importance for increasing the energy density of energy storage systems to power electric aircraft and beyond. Carbon fluoride (CFx) cathodes are characterized by high specific capacity and energy density (865 mAh g-1 and 2180 Wh kg-1, respectively). Preventing the crystallization of LiF with an intermediate and lowering the energy barrier from LiF to CFx is expected to render the Li/CFx battery reversible. In this study, taking the advantage of a high-voltage-stable all-fluorinated electrolyte containing the boron-based anion receptor tris(trimethylsilyl)borate (TMSB), a rechargeable Li/CFx battery was realized with a reversible capacity of 465.9 mAh g-1 and an energy density of 1183.9 Wh kg-1, approximately 53% of that in the first discharge. After the first discharge, the charge-discharge profile featured rechargeable characteristics. In situ X-ray diffraction, ex situ soft X-ray absorption spectroscopy, pair distribution function analysis, and other measurements confirmed the generation and decomposition of Li-F and C-F bonds during cycling. Density functional theory calculations and nuclear magnetic resonance spectroscopy confirmed that TMSB serves as an anion carrier through the generation of a [TMSB-F]- complex, facilitating the conversion reactions during cycling. This study demonstrated a facile and low-cost approach for realizing high-energy-density, reversible Li/CFx batteries.

Operando Building of a Superior Interface Hybrid Film Enables Chemomechanically Durable Co-Free Ni-Rich Cathodes.

The Co-free Ni-rich layered cathodes become pivotal to reduce cost and increase benefit toward next-generation Li-ion batteries yet raise a major challenge for their extremely fragile cathode-electrolyte interface (CEI) film. Herein, we report the in situ construction of the Si/B-enriched organic-inorganic hybrid CEI films on LiNi0.9Mn0.1O2 (NM91) with the assistance of tris(trimethylsilyl) borate (TMSB) additive. The hybrid film exhibits superior Young's modulus, mechanical strength, and ductility, which greatly dissipate the microstrain of Co-free Ni-rich cathodes under various states of charge with high structural integrity. Furthermore, the surface oxygen anions have been significantly stabilized by bonding with the Si and B ions of TMSB with high safety. These merits enable a durable Co-free Ni-rich layered cathode with 96.9% and 87.7% capacity retentions (versus 72.7% and 70.2% of NM91) at a high rate of 5C and a high-temperature of 55 °C after 100 cycles. In a pouch-type full cell, 88.8% of initial capacity is still maintained after cycling at 1C for 500 times, greatly expediting the development and application of Co-free Ni-rich layered cathodes.

570 Whkg⁻1-Grade Lithium Metal Pouch Cell with 4.9V Highly Li+ Conductive Armor-Like Cathode Electrolyte Interphase via Partially Fluorinated Electrolyte Engineering.

Lithium-rich manganese-based layered oxides (LRMOs) are promisingly used in high-energy lithium metal pouch cells due to high specific capacity/working voltage. However, the interfacial stability of LRMOs remains challenging. To address this question, a novel armor-like cathode electrolyte interphase (CEI) model is proposed for stabilizing LRMOcathode at 4.9V by exploring partially fluorinated electrolyte formulation. The fluoroethylene carbonate (FEC) and tris (trimethylsilyl) borate (TMSB) in formulated electrolyte largely contribute to the formation of 4.9V armor-like CEI with LiBxOy and LixPOyFz outer layer and LiF- and Li3PO4-rich inner part. Such CEI effectively inhibits lattice oxygen loss and facilitates the Li+ migration smoothly for guaranteeing LRMO cathode to deliver superior cycling and rate performance. As expected, Li||LRMO batteries with such electrolyte achieve capacity retention of 85.7% with high average Coulomb efficiency (CE) of 99.64% after 300 cycles at 4.8V/0.5 C, and even obtain capacity retention of 87.4% after 100 cycles at higher cut-off voltage of 4.9V. Meanwhile, the 9 Ah-class Li||LRMO pouch cells with formulated electrolyte show over thirty-eight stable cycling life with high energy density of 576Wh kg-1 at 4.8V.

Improved Interface Construction on Anode and Cathode for Na-Ion Batteries Using Ultralow-Concentration Electrolyte Containing Dual-Additives.

Compared with Li+, Na+ with a smaller stokes radius has faster de-solvation kinetics. An electrolyte with ultralow sodium salt (0.3 M NaPF6) is used to reduce the cell cost. However, the organic-dominated interface, mainly derived from decomposed solvents (SSIP solvation structure), is defective for the long cycling performance of sodium ion batteries. In this work, the simple application of dual additives, including sodium difluoro(oxalato)borate (NaDFOB) and tris(trimethylsilyl)borate (TMSB), is demonstrated to improve the cycling performance of the hard carbon/NaNi1/3Fe1/3Mn1/3O2 cell by constructing interface films on the anode and cathode. A significant improvement on cycling stability has been achieved by incorporating dual additives of NaDFOB and TMSB. Particularly, the capacity retention increased from 17 % (baseline) to 79 % (w/w, 2.0 wt % NaDFOB) and 83 % (w/w, 2.0 wt % NaDFOB and 1.0 wt % TMSB) after 200 cycles at room temperature. Insight into the mechanism of improved interfacial properties between electrodes and electrolyte in ultralow concentration electrolyte has been investigated through a combination of theoretical computation and experimental techniques.

Composite electrolytes engineered by anion acceptors for boosted high-voltage solid-state lithium metal batteries

Solid-state batteries (SSBs) are considered as the most promising option to replace commercial lithium-ion batteries due to their ability to address the flammability of liquid organic electrolytes and facilitate the energy density of lithium batteries. Herein, by introducing tris(trimethylsilyl) borate (TMSB) as anion acceptors, we successfully develop the light and thin electrolyte (TMSB-PVDF-HFP-LLZTO-LiTFSI, PLFB) with a wide voltage window to couple the lithium metal anode with the high-voltage cathodes. Consequently, as-prepared PLFB can greatly boost the generation of free Li+ and improve the Li+ transference numbers (tLi+=0.92) at room temperature. Moreover, combined with theoretical calculation and experimental results, the changes in the composition and properties of the composite electrolyte membrane with the addition of anionic receptors are systematically studied, which further implies the intrinsic mechanism of the stability difference. In addition, the PLFB-based SSB assembled by LiNi0.8Co0.1Mn0.1O2 cathode and lithium anode exhibits a high capacity retention of 86% after loop 400 cycles. This investigation on boosted battery performance by immobilized anions not only contributes to the directional construction of dendrite-free and lithium-ion permeable interface, but also brings new opportunities for the screening and design of the next generation of high-energy SSBs.

Improved interfacial properties of LiNi0.8Co0.15Al0.05O2 cathode by tris(trimethylsilyl) borate as an electrolyte additive to inhibit HF formation

Tris(trimethylsilyl)borate (TMSB) is selected as an electrolyte additive in Li/LiNi0.8Co0.15Al0.05O2 cell due to its low oxidation potential. Its positive effect on improving the performances of the cells is analyzed by nuclear magnetic resonance, X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma. The results show that the oxidative decomposition products of TMSB are involved in the formation of cathode electrolyte interface film. The trimethylsilyl group can react with HF to form trimethylsilyl fluoride and dimethyldifluorosilane, which reduces transition metal leaching through HF on LiNi0.8Co0.15Al0.05O2 (NCA) cathode. Meanwhile, a thinner interfacial film with a lower LiF content is formed, which contributes to the structural stability of NCA and inhibits the decomposition of the electrolyte. As a result, the NCA cathode in the electrolyte containing 1% TMSB shows higher cycling stability and rate performance, and has a lower impedance. Even at 1 C after 200 cycles, it still provides capacity retention with 86.0% compared to 67.2% for the cathode in baseline electrolyte. This work could provide an idea for the use of silicon-boron compounds as electrolyte additive to improve the electrochemical performances of ternary cathodes.

Adjusting the solvation structure with tris(trimethylsilyl)borate additive to improve the performance of LNCM half cells

Tris(trimethylsilyl)borate (TMSB) has been intensively studied to improve the performances of lithium-ion batteries. However, it is still an interesting issue needed to be resolved for the research on the Li+ solvation structure affected by TMSB additive. Herein, the electrochemical tests, quantum chemistry calculations, potential-resolved in-situ electrochemical impedance spectroscopy measurements and surface analyses were used to explore the effects of Li+ solvation structure with TMSB additive on the formation of the cathode electrolyte interface (CEI) film in LiNi0.8Co0.1Mn0.1O2/Li half cells. The results reveal that the TMSB additive is easy to complex with Li+ ion, thus weaken the intermolecular force between Li+ ions and ethylene carbonate solvent, which is benefit for the cycle performance. Besides, the changed Li+ solvation structure results in a thin and dense CEI film containing compounds with Si–O and B–O bonds which is favorable to the transfer of Li+ ions. As a result, the performances of the LNCM811/Li half cells are effectively improved. This research provides a new idea to construct a high-performance CEI film by adjusting the Li+ solvation structures.

Tris(trimethylsilyl) borate as electrolyte additive alleviating cathode electrolyte interphase for enhanced lithium-selenium battery

Lithium-selenium (Li-Se) batteries have attracted increasing attentions in recent years because of their high energy density and theoretical capacity. One of the keys that influences the cycle stability of Se cathode is the formation of a stable cathode electrolyte interphase (CEI) film between the cathode material and electrolyte. In this work, we report utilizing tris(trimethylsilyl) borate (TMSB) as electrolyte additive to promote the formation of stable CEI film for enhanced Li-Se battery. The TMSB containing electron-deficient boron atoms easily adsorb electron-rich F− and PFx− to form polyanionic groups, which suppress the formation of insulating LiF in the CEI film, promoting the conductivity and stability of the cathode. Furthermore, the TMSB adsorbing PFx− releases more active Li+ for reaction to improve the capacity. These largely improve the compatibility of the electrolyte and the electrode material interface, significantly reducing the interface impedance and increasing the rate capability. As the result, the system with 1 wt% TMSB exhibits a high specific discharge capacity of 462 mA h g –1 at 1 C after 500 cycles, showing 130% improvement for the cathode without TMSB. Our work here confirms that TMSB as electrolyte additive can effectively improve the electrochemical performance of Li-Se batteries.

Enabling high-performance aqueous rechargeable Li-ion batteries through systematic optimization of TiS2/LiFePO4 full cell

The conventional lithium-ion batteries (LIBs) have dominated the portable electronics markets; however, inherent limitations have raised concerns over their cost, safety, and greenness in large scale energy storage applications. Taking advantage of the recently developed “Water-in-Salt” electrolyte (WiSE), an aqueous lithium-ion battery of TiS2/LiFePO4 (LFP) is demonstrated. The effects of potential window, addition of tris(trimethylsilyl) borate (TMSB) salt, and the choice of current collector on cell performance are investigated. The aqueous TiS2/LFP cell delivers an energy density of 65 Wh kg−1, based on the total mass of electrodes. The presence of TMSB additive enhances the capacity, stability, and efficiency of the cell. Compared to the control cell, the capacity increases by 34%, SEI layer resistance decreases by 1.7 times, and the charge transfer resistance decreases by 7 times, yielding high coulombic efficiency of 99.9% and capacity retention of 70% after 100 cycles. A safe potential window of 0.01–1.6 V, 0.1 wt% TMSB in WiSE, and stainless-steel current collector on the cathode and titanium on the anode offer the most stable cycling. The combination of low-cost electrodes, safer and greener electrolyte, and high coulombic efficiency make this new aqueous battery promising for large scale energy storage systems.

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

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/Li2RuO3) 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 LiPF6 salt. The decomposition of the LiPF6 salt and the formation of Li2CO3 and -CO2 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 (O- or O0.5-) 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/Li2RuO3 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.

Operando Fourier Transform Infrared Investigation of Cathode Electrolyte Interphase Dynamic Reversible Evolution on Li1.2Ni0.2Mn0.6O2.

One of the keys to the cycling stability of electrode materials is the formation of a stable interface film on cathode materials, which is called a cathode electrolyte interphase (CEI). For a Li/Mn-rich cathode, especially, the high working voltage will cause an extremely unstable electrolyte environment, becoming a challenge for the stable interface film formation. In this work, an operando-attenuated total reflection-Fourier transform infrared (ATR-FTIR) technique is developed to monitor in real time the dynamic mechanism of CEI formation in a carbonate-based electrolyte with or without the moderate additive tris(trimethylsilyl)borate (TMSB), which could promote the formation and stability of high-quality CEI films when it charges to 4.8 V. It is interesting that the components of CEI are basically generated in the first cycle owing to ethylene carbonate (EC) priority decomposition. Besides, the presence of TMSB can suppress the decomposition of EC in part and modify the stability of the CEI film. This is because TMSB containing an electron-deficient boron atom can easily combine with an electron-rich F- and PF6- forming a polyanion group initially, which will weaken the electrostatic force between the anionic groups and EC to reduce the concentration of EC on the cathode surface and prevent the continuous decomposition of EC at a high voltage. X-ray photoelectron spectroscopy also verifies the presence of polyanion groups and their further participation in CEI formation. This work highlights the dynamical stability of CEI modified by moderate TMSB and the formation mechanism of this dynamical change during cycling characterized by the operando ATR-FTIR technique, which paves the way for a better understanding of the complex and hard-characterized cathode interface reactions.

S-containing and Si-containing compounds as highly effective electrolyte additives for SiOx -based anodes/NCM 811 cathodes in lithium ion cells

Recently, high-energy density cells containing nickel-rich cathodes and silicon-based anodes have become a practical solution for increasing the driving range of electric vehicles. However, their long-term durability and storage performance is comparatively poor because of the unstable cathode-electrolyte-interphase (CEI) of the high-reactivity cathode and the continuous solid-electrolyte-interphase (SEI) growth. In this work, we study several electrolyte systems consisting of various additives, such as S-containing (1,3,2-dioxathiolane 2,2-dioxide (DTD), DTD + prop-1-ene-1,3-sultone (PES), methylene methanedisulfonate (MMDS)) and Si-containing (tris(trimethylsilyl) phosphate (TTSP) and tris(trimethylsilyl) borate (TMSB)) compounds, in comparison to the baseline electrolyte (BL = 1.0 M LiPF6 + 3:5:2 w-w:w EC: EMC: DEC + 0.5 wt% lithium difluoro(oxalato)borate (LiDFOB) + 2 wt% lithium bis(fluorosulfonyl)imide (LiFSI) + 2 wt% fluoroethylene carbonate (FEC) + 1 wt% 1,3-propane sultone (PS)). Generally, electrolytes with Si-containing additives, particularly BL + 0.5% TTSP, show a lower impedance increase in the full cell, better beginning-of-life (BOL) performance, less reversible capacity loss through long-term cycles and better storage at elevated temperatures than do electrolytes with S-containing additives. On the contrary, electrolytes with S-containing additives exhibit the advantage of low SEI impedance but yield a worse performance in the full cell than do those with Si-containing additives. The difference between two types of additives is attributed to the distinct function of the electrodes, which is characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS), which was performed on full cells and half cells with fresh and harvested electrodes.

Enhancement in cycling stability of LiNi0.5Mn1.5O4/Li cell under high temperature in gel polymer electrolyte system by Tris(trimethylsilyl) borate additive

Tris(trimethylsilyl) borate (TMSB) has been taken as solid electrolyte interface forming additive in carbonated liquid electrolyte of current lithium ion battery, but it has not been applied in Gel Polymer Electrolyte (GPE) yet. In this investigation, TMSB is selected to enhance the cyclic performance of high voltage cathode LiNi0.5Mn1.5O4 under elevated temperature in traditional poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-HFP)) based GPE system. By addition of 1 wt% TMSB into GPE, 79% capacity retention ratio is kept at room temperature after 1000 cycles for Li/LiNi0.5Mn1.5O4 coin cell, whose retention value is almost the same as the GPE without additive. However, the discharge capacity retention is improved to 86% after 230 cycles with TMSB additive at high temperature of 55 °C, compared with 75% retention for the GPE without additive. From the physical and chemical characterization, it finds that the improvement in electrochemical performance of GPE with additive is caused by the formation of thin and uniform solid electrolyte interface layer between the GPE and cathode material, which is beneficial to inhibit the further decomposition of liquid component in GPE system and keep the structure integrity of LiNi0.5Mn1.5O4 cathode under high temperature environment.

Improving cycling performance of LiCoPO4 cathode material by adding tris(trimethylsilyl) borate as electrolyte additive

Tris(trimethylsilyl) borate (TMSB) is used as electrolyte additive to overcome the severe capacity fading of LiCoPO4 cathode at high voltage. The presence of TMSB effectively improves the cyclic stability of LiCoPO4 cathode in Ethylene carbonate (EC)-based electrolyte between 3V and 5V, when the electrolyte contains with 1wt% TMSB shows the best cycle performance. For instance, LiCoPO4 cathode delivers an initial discharge capacity of 144mAhg−1 at 0.1C and with a capacity retention of 76% after 50cycles, while it's only 132mAhg−1 and 45% for that in normal electrolyte without TMSB. The linear sweep voltammetry (LSV) and cyclic voltammetry (CV) results indicate that TMSB oxidizes preferentially to normal electrolyte and forms a stable SEI film on LiCoPO4 surface at the first cycle which effectively reduces the electrode polarization. The electrochemical impedance spectroscopy (EIS) results reveal that the stable SEI film alleviates the growth of SEI layer on the LiCoPO4 surface and relieves the resistance increase to facilitate Li-ion transfer the interface between electrode and electrolyte. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveal that a 20nm film can be observed on the cathode surface after 50cycles as the electrolyte containing with 1wt% TMSB. Moreover, X-ray photoelectron spectrometer (XPS) patterns confirm that the oxidation products of TMSB participate in the SEI film formation. The enhancement of electrochemical performances is attributed to the thin and steady protective SEI film that originates from TMSB, which stabilizes the interface of the cathode and electrolyte, suppresses the continuous decomposition of normal electrolyte at 5V high voltage and relieves the resistance increase to facilitate Li-ion transfer at the interface during the cycling process.

A comparative study of Si-containing electrolyte additives for lithium ion battery: Which one is better and why is it better

Abstract Influence of two Si-containing electrolyte additives, tris(trimethylsilyl)borate (TMSB) and tris(trimethylsilyl)phosphate (TMSP), on the cyclic stability of high voltage LiNi0.5Mn1.5O4 electrode has been systematically studied in this work. The capacity retention of LiNi0.5Mn1.5O4 cycling in STD (1M LiPF6/EC: EMC = 3:7), TMSB- and TMSP-containing electrolytes is 23%, 85% and 71% after 600 cycles at 1C rate, respectively, revealing that the ability of TMSB on improving the cyclic performance of LiNi0.5Mn1.5O4 is superior to that of TMSP. Experimental and theoretical characterizations show that the preferential reaction of both TMSB and TMSP generates thin and uniform film on LiNi0.5Mn1.5O4 surface, which effectively suppress the continuous oxidation reaction of electrolyte. While the film generated from TMSB, which contains B and Si-rich compounds, shows better ability on restraining the growth of interfacial resistance during cycling, resulting in better cyclic stability of LiNi0.5Mn1.5O4 than that of TMSP.

Tris(trimethylsilyl) borate as an electrolyte additive for high-voltage lithium-ion batteries using LiNi1/3Mn1/3Co1/3O2 cathode

The influence of tris(trimethylsilyl) borate (TMSB) as an electrolyte additive on lithium ion cells have been studied using Li/LiCo1/3Ni1/3Mn1/3O2 cells at a higher voltage, 4.7V versus Li/Li+. 1wt% TMSB can dramatically reduce the capacity fading that occurs during cycling at room temperature (RT) and elevated temperature (60°C). After 150 cycles at 1C rate (1C=278mAh/g), the capacity retention of Li/LiCo1/3Ni1/3Mn1/3O2 is up to near 72% in the electrolyte with TMSB added, while it is only about 35% in the baseline electrolyte. The electrochemical behaviors, the surface chemistry and structure of Li/LiCo1/3Ni1/3Mn1/3O2 cathode are characterized with charge/discharge test, linear sweep voltammetry (LSV), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), thermal gravimetric analyses (TGA), scanning electron microscope (SEM) and transmission electron microscopy (TEM). These analysis results reveal that the addition of TMSB is able to protectively modify the electrode CEI film in a manner that suppresses electrolyte decomposition and degradation of electrode surface structure, even though at both a higher voltage of 4.7V and an elevated temperature of 60°C.

Application of tris(trimethylsilyl)borate to suppress self-discharge of layered nickel cobalt manganese oxide for high energy battery

Tris(trimethylsilyl)borate (TMSB) is applied to suppress the self-discharge of charged LiNi1/3Co1/3Mn1/3O2 (LNCM) under high potential. The contribution of TMSB is understood via physical and electrochemical characterizations. It is found that the charged LNCM under 4.5V suffers serious self-discharge: potential drops to 0.5V and crystal structure collapses, but this self-discharge is effectively suppressed by applying TMSB in a standard (STD) electrolyte. Different from the failure from cycling, which is caused mainly by the electrochemical oxidation decomposition of electrolyte, the self-discharge results from the interaction between charged LNCM and electrolyte. TMSB is preferentially oxidized in comparison with STD electrolyte, generating a solid electrolyte interphase film on LNCM, which avoids the direct contact between LNCM and electrolyte and thus suppresses the self-discharge of the charged LNCM.

Tris(trimethylsilyl)borate as an electrolyte additive for improving interfacial stability of high voltage layered lithium-rich oxide cathode/carbonate-based electrolyte

Tris(trimethylsilyl)borate (TMSB) is used as an electrolyte additive for high voltage lithium-rich oxide cathode of lithium ion battery. The interfacial natures of Li[Li0.2Mn0.54Ni0.13Co0.13]O2/carbonate-based electrolyte are investigated with a combination of electrochemical measurements and physical characterizations. Charge/discharge tests show that the cyclic performance of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 in a mixed carbonate electrolyte is significantly improved by using TMSB. After 200 cycles between 2 V and 4.8 V (vs. Li/Li+) at 0.5 C rate, the capacity retention of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 is only 19% in the blank electrolyte, while it is improved to 74% when 0.5% TMSB is applied. The results from physical characterizations demonstrate that this excellent cyclic performance is attributed to the improved interfacial stability of Li[Li0.2Mn0.54Ni0.13Co0.13]O2/electrolyte due to the thin and protective film generated by TMSB.

Tris (trimethylsilyl) borate (TMSB) as a cathode surface film forming additive for 5 V Li/LiNi0.5Mn1.5O4 Li-ion cells

The cycling performance of 5 V Li/LiNi0.5Mn1.5O4 cells with 1.0 M LiPF6 EC/DMC (1/2, v/v) with and without TMSB (0.2, 0.5, 1.0 and 2.0wt.%) has been investigated. After 200 cycles, the cells with 1.0wt.% TMSB have superior cycling performance with 95.3% capacity retention; while the cells with baseline electrolyte only maintain 84.4% capacity retention. The cells with 1.0wt.% TMSB containing electrolyte have lower impedance after cycling at high voltage. In addition, the TMSB added cells show superior elevated temperature storage performance, the discharge capacity is 122.1mAhg−1 and 109.9mAhg−1 for the cells with and without TMSB after storage at 60°C for a week at fully charged state, respectively. In order to further understand the effects of TMSB on LiNi0.5Mn1.5O4 cathode upon cycling at high voltage, scanning electron microscopy (SEM), thermal-gravimetric analysis (TGA), transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscope (XPS), Fourier transform infrared spectroscopy (FTIR), and inductively coupled plasma mass spectrometry (ICP-MS) analysis were conducted after the cycling test. The results indicate that the use of TMSB can form a stable and compact film on the surface of the LiNi0.5Mn1.5O4 electrode, which inhibits the continuous decomposition of the electrolyte and reduces the dissolution of Mn and Ni from the bulk cathode material.

Self-discharge suppression of 4.9 V LiNi0.5Mn1.5O4 cathode by using tris(trimethylsilyl)borate as an electrolyte additive

In this paper, tris(trimethylsilyl)borate (TMSB) is evaluated as an electrolyte additive for the self-discharge suppression of 4.9 V LiNi0.5Mn1.5O4 cathode for lithium ion battery. The effect of TMSB on the surface properties of LiNi0.5Mn1.5O4 is investigated via linear sweep voltammetry (LSV), cyclic voltammetry (CV), chronoamperometry (CA), charge–discharge test, electrochemical impedance spectra (EIS), scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma atomic emission spectrometer (ICP-AES) and Fourier transform infrared spectroscopy (FTIR). It is found that the LiNi0.5Mn1.5O4 cathode charged to 4.9 V (vs. Li/Li+) suffers a serious self-discharge in 1 mol L−1 LiPF6–EC/DMC (1:2, in weight), which can be suppressed effectively by adding 1 wt.% TMSB into the electrolyte. After storage for 20 days, the voltage of the charged cathode decreases from 4.7 to 0.5 V (vs. Li/Li+) in the additive-free electrolyte, while that remains almost unchanged in the TMSB-containing electrolyte. The self-discharge suppression of the charged LiNi0.5Mn1.5O4 cathode results from the preferential oxidation of TMSB and the subsequent formation of a protective solid electrolyte interphase film, which prevents electrolyte decomposition and protects LiNi0.5Mn1.5O4 from destruction.