Lithium- and manganese-rich layered-oxides (LMR-NMC) have potential application for electric vehicles due to the high energy density. Electrochemical measurements and ex-situ surface analysis of ...cells containing Li1.2Ni0.15Mn0.55Co0.1O2-based positive electrodes and graphite-based negative electrodes has been conducted. Electrochemical cycling reveals significant capacity fade and voltage decrease after 1500 cycles. Ex-situ surface analysis including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) were conducted for cells with long term cycling at 30 degree C. The surface analysis supports the formation of surface film on both cathodes and anodes after formation cycling. Upon long term cycling, both the cathode and anode surface films become thicker although more significant changes appear to be occurring to the anode. Fresh LMR-NMC powder has been stored in the presence of electrolyte, 1.2 M LiPF6 in EC/EMC 3:7, at 85 degree C for 7 days. The surface film on the LMR-NMC powder after storage is similar to the surface film after cycling. The presence of the LMR-NMC powder inhibits the thermal decomposition of the electrolyte.
The formation of lithiophobic inorganic solid electrolyte interphase (SEI) on Li anode and cathode electrolyte interphase (CEI) on the cathode is beneficial for high‐voltage Li metal batteries. ...However, in most liquid electrolytes, the decomposition of organic solvents inevitably forms organic components in the SEI and CEI. In addition, organic solvents often pose substantial safety risks due to their high volatility and flammability. Herein, an organic‐solvent‐free eutectic electrolyte based on low‐melting alkali perfluorinated‐sulfonimide salts is reported. The exclusive anion reduction on Li anode surface results in an inorganic, LiF‐rich SEI with high capability to suppress Li dendrite, as evidenced by the high Li plating/stripping CE of 99.4% at 0.5 mA cm−2 and 1.0 mAh cm−2, and 200‐cycle lifespan of full LiNi0.8Co0.15Al0.05O2 (2.0 mAh cm−2) || Li (20 µm) cells at 80 °C. The proposed eutectic electrolyte is promising for ultrasafe and high‐energy Li metal batteries.
For the first time, an electrolyte solely comprising inorganic salts is reported for 4.0‐V Li metal batteries. The complete absence of organic solvents brings about new implications for cell safety, interphase chemistry, and overall performance. For future advances in this direction, a principle for composition design is also proposed.
Micro-sized silicon anodes can significantly increase the energy density of lithium-ion batteries with low cost. However, the large silicon volume changes during cycling cause cracks for both ...organic-inorganic interphases and silicon particles. The liquid electrolytes further penetrate the cracked silicon particles and reform the interphases, resulting in huge electrode swelling and quick capacity decay. Here we resolve these challenges by designing a high-voltage electrolyte that forms silicon-phobic interphases with weak bonding to lithium-silicon alloys. The designed electrolyte enables micro-sized silicon anodes (5 µm, 4.1 mAh cm
) to achieve a Coulombic efficiency of 99.8% and capacity of 2175 mAh g
for >250 cycles and enable 100 mAh LiNi
Co
Al
O
pouch full cells to deliver a high capacity of 172 mAh g
for 120 cycles with Coulombic efficiency of >99.9%. The high-voltage electrolytes that are capable of forming silicon-phobic interphases pave new ways for the commercialization of lithium-ion batteries using micro-sized silicon anodes.
Lithium cyano tris(2,2,2-trifluoroethyl) borate (LCTFEB) has been synthesized and investigated as a new electrolyte additive for high-performance lithium metal batteries. LCTFEB is prepared by the ...reaction of tris(2,2,2-trifluoroethyl) borate with lithium cyanide. The incorporation of LCTFEB into a carbonate-based electrolyte has been investigated. The electrochemical performance of NCM523/Li cells and symmetric Li/Li cells is significantly improved upon the incorporation of LCTFEB (5 wt %) into the electrolyte. Various characterizations of the lithium metal morphology and the solid electrolyte interphase (SEI) on the lithium metal anode have been conducted using field-emission scanning electron microscopy, cryogenic transmission electron microscopy, and X-ray photoelectron spectroscopy, suggesting the generation of a thin (∼10 nm) LiF-rich SEI with low concentrations of B and N compounds. The different SEI structures are formed by the preferential reductive decomposition of LCTFEB, resulting in improved electrochemical performance. The new electrolyte additive provides insight into innovative approaches for multifunctional electrolyte additive design.
Anion solvation in electrolytes can largely change the electrochemical performance of the electrolytes, yet has been rarely investigated. Herein, three anions of bis(trifluoromethanesulfonyl)imide ...(TFSI), bis(fluorosulfonyl)imide (FSI), and derived asymmetric (fluorosulfonyl)(trifluoro‐methanesulfonyl)imide (FTFSI) are systematically examined in a weakly Li+ cation solvating solvent of bis(3‐fluoropropyl)ether (BFPE). In‐situ liquid secondary ion mass spectrometry demonstrates that FTFSI− and FSI− anions are associated with BFPE solvent, while weak TFSI−/BFPE cluster signals are detected. Molecular modeling further reveals that the anion–solvent interaction is accompanied by the formation of H‐bonding‐like interactions. Anion solvation enhances the Li+ cation transfer number and reduces the organic component in solid electrolyte interphase, which enhances the Li plating/stripping Coulombic efficiency at a low temperature of −30 °C from 42.4% in TFSI‐based electrolytes to 98.7% in 1.5 m LiFTFSI and 97.9% in LiFSI‐BFPE electrolytes. The anion–solvent interactions, especially asymmetric anion solvation also accelerate the Li+ desolvation kinetics. The 1.5 m LiFTFSI‐BFPE electrolyte with strong anion–solvent interaction enables LiNi0.8Mn0.1Co0.1O2 (NMC811)||Li (20 µm) full cell with stable cyclability even under −40 °C, retaining over 92% of initial capacity (115 mAh g−1, after 100 cycles). The anion–solvent interactions insights allow to rational design the electrolyte for lithium metal batteries and beyond to achieve high performance.
Anion solvation is demonstrated as a new direction to rational design the electrolyte for lithium metal batteries and beyond to achieve high performance. The designed electrolyte with strong anion–solvent interaction enables 2.0 mAh cm−2 NMC811||Li (20 µm) full cells to achieve excellent high voltage and low temperature performance, retaining over 92% of initial capacity after 100 cycles even under −40 °C.
Thermal reactions between 1.0 M LiPF6 in 1:1:1 ethylene carbonate/dimethyl carbonate/diefhyl carbonate and metal-oxide cathode particles were investigated by analyzing both the liquid electrolyte and ...solid cathode particles through the combined use of nuclear magnetic resonance spectroscopy, gas chromatography with mass selective detection, scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The reactions between the electrolyte and cathode particles inhibit the thermal decomposition of the electrolyte and modify the surface of the cathode particles. The Li2C03 on the surface of the metal oxides is removed and replaced by a complex mixture including poly(ethylene oxide), polycarbonate, ROC02Li, LiF, and LixPOyFz,. Higher surface concentration of Li2C03 on LiNi0.8Co0.2O2 allows a fragile temperature-dependent equilibrium to be established, accounting for the thermal stability of the electrolyte. Higher temperature leads to more LixPOYFz and less Li2C03 on the surface. With LiCo02, no equilibrium is established due to lower surface concentration of Li2C03. Consequently, thermal reactions of the electrolyte with LiCo02 generate decomposition products, including LixPOyFz and cobalt fluorides on the surface and bulk electrolyte decomposition. Independent addition of Li2C03 enhances the thermal stability of the LiPF6-based electrolyte, confirming the thermal-stabilizing properties of Li2C03 surface films. The addition of a carbonate solution of PF5 to LiNi0.8Co0.2O2 generates LiPF6 in the solution and LixPOyFz, on the surface.
The beneficial role of lithium bis(trimethylsilyl) phosphate (LiTMSP), which may act as a novel bifunctional additive for high-voltage LiNi1.5Mn0.5O4 (LNMO)/graphite cells, has been investigated. ...LiTMSP is synthesized by heating tris(trimethylsilyl) phosphate with lithium tert-butoxide. The cycle performance of LNMO/graphite cells at 45 °C significantly improved upon incorporation of LiTMSP (0.5 wt %). Nuclear magnetic resonance analysis suggests that the trimethylsilyl (TMS) group in LiTMSP can react with hydrogen fluoride (HF), which is generated through the hydrolysis of lithium hexafluorophosphate (LiPF6) by residual water in an electrolyte solution or water generated via oxidative electrolyte decomposition reactions to form TMS fluoride. Inhibition of HF leads to a decrease in the concentration of transition-metal ion-dissolution (Ni and Mn) from the LNMO electrode, as determined by inductively coupled plasma mass spectrometry. In addition, the generation of the superior passivating surface film derived by LiTMSP on the graphite electrode, suppressing further electrolyte reductive decomposition as well as deterioration/reformation caused by migrated transition metal ions, is supported by a combination of chronoamperometry, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. Furthermore, a LiTMSP-derived surface film has better lithium ion conductivity with a decrease in resistance of the graphite electrode, as confirmed by electrochemical impedance spectroscopy, leading to improvement in the rate performance of LNMO/graphite cells. The HF-scavenging and film-forming effects of LiTMPS are responsible for the less polarization of LNMO/graphite cells enabling improved cycle performance at 45 °C.
Cellulose is hydrolyzed to glucose, which is further converted to levulinic acid in the presence of Nafion, as a surface supported acid catalyst. The addition of simple alkali metal halide salts, ...including NaCl, provides significant enhancement to the yield. The catalyst can be recycled suggesting possible extension into a continuous flow reactor for the synthesis of the biofuel precursors.
The physico-chemical properties of poly (1-pyrenemethyl methacrylate) (PPy) are presented with respect to its use as a binder in a Si composite anode for Li-ion batteries. PPy thin-films on Si(100) ...wafer and Cu model electrodes are shown to exhibit superior adhesion as compared to conventional polyvinylidene difluoride (PVdF) binder. Electrochemical testing of the model bi-layer PPy/Si(100) electrodes in a standard organic carbonate electrolyte reveal higher electrolyte reduction current and an overall irreversible cathodic charge consumption during initial cycling versus the uncoated Si electrode. The PPy thin-film is also shown to impede lithiation of the underlying Si. XAS, AFM, TGA and ATR-FTIR analysis indicated that PPy binder is both chemically and electrochemically stable in the cycling potential range however significant swelling is observed due to a selective uptake of diethyl carbonate (DEC) from the electrolyte. The increased concentration of DEC and depletion of ethylene carbonate (EC) at the Si/PPy interface leads to continuous decomposition of the electrolyte and results in non-passivating behavior of the Si(100)/PPy electrode as compared to pristine silicon. Consequently, PPy binder improves the mechanical integrity of composite Si anodes but it influences mass transport at the Si(100)/PPy interface and alters electrochemical response of silicon during cycling in an adverse manner.
•PPy binder shows improved adhesion to Si and Cu with regard to PVdF and PAALi.•PPy thin film alters electrochemical response of the Si electrode.•Mechanical and interfacial properties of Si electrode depend on PPy binder topology.
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