Decomposition Of LiPF6 Research Articles

Dual‐Salt Electrolyte with Synergistic Effect for Lithium Metal Batteries with Prolonging Cyclic Performance

AbstractAlong with the booming development of human society, the commercial lithium‐ion battery cannot satisfy increasing energy demand for the insufficient energy density, which is attributed to the limited theoretical capacity (372 mAh g−1) of graphite anode. Logically, lithium (Li) metal, which can deliver ultrahigh theoretical capacity of 3860 mAh g−1 and lowest electrochemical potential of −3.04 V versus standard hydrogen electrode, is regarded as the “holy grail” for next‐generation energy storage systems with high energy density. Nevertheless, the practical application of Li metal batteries is hampered by low Coulombic efficiency and poor cyclic performance caused by the dendritic electrodeposition. Herein, a kind of novel carbonate‐based electrolyte with a dual‐salt of hexafluorophosphate (LiPF6) and lithium borate difluoroxalate (LiDFOB) for stable Li anode is designed and demonstrated. The introduction of LiDFOB can not only uniform electrodeposition of Li to promote Coulombic efficiency and cycle stability, but also can suppress decomposition of LiPF6 to passivate cathode surfaces. Taking this synergistic effect, Li metal batteries with the high‐capacity ternary cathode of LiNi0.8Co0.1Mn0.1O2 (NMC811) exhibits outstanding cyclic performance with high‐rate capability. Encouragingly, the posted electrolyte is expected to foster the commercial application of Li metal batteries for pursuing high‐energy density.

Understanding the Role of Commercial Separators and Their Reactivity toward LiPF6 on the Failure Mechanism of High‐Voltage NCM523 || Graphite Lithium Ion Cells

AbstractNCM523 || graphite lithium ion cells operated at 4.5 V are prone to an early “rollover” failure, due to electrode cross‐talk, that is, transition metal (TM = Mn, Ni, and Co) dissolution from NCM523 and deposition at graphite, subsequent formation of Li metal dendrites, and, in the worst case, generation of (micro‐)short‐circuits by dendrites growing to the cathode. Here, the impact of different separators on the high‐voltage performance of NCM523 || graphite cells is elucidated focusing on the separators’ structural properties (e.g., membrane vs fiber) and their reactivity toward LiPF6 (e.g., ceramic‐coated separators). First, the separator architecture has a major impact on cycle life. Fiber‐structured separators can prevent the “rollover” failure by a more homogeneous deposition of TMs and formation of Li metal dendrites, thus, hindering penetration of dendrites to the cathode. In contrast, porous membrane‐structured separators cannot prevent the cell failure due to inhomogeneous TM deposits/Li metal dendrites. Second, it is demonstrated that different types of ceramic‐coated separators (Boehmite (γ‐AlO(OH)) vs α‐Al2O3) exhibit different reactivities toward LiPF6. While α‐Al2O3 shows a minor reactivity toward LiPF6, the γ‐AlO(OH) coating leads to in situ formation of the beneficial difluorophosphate anion in high amounts due the high reactivity toward LiPF6 decomposition, which significantly improves cycle life.

Improving High‐Voltage Performance of a LiNi0.5Co0.2Mn0.3O2 Cathode with Triallyl Phosphite as an Electrolyte Additive

AbstractTriallyl phosphite (TAPi) is studied as an electrolyte additive for high‐voltage LiNi0.5Co0.2Mn0.3O2 cathodes. Theoretical calculations combined with linear sweep voltammetry (LSV) tests demonstrate that TAPi tends to be preferentially oxidized and suppresses the decomposition of traditional carbonate‐based electrolytes. In addition, the hydrolysis of LiPF6 salt in the electrolyte is investigated by 19F nuclear magnetic resonance spectra, which prove that TAPi inhibits the decomposition of LiPF6. The results of charge/discharge measurements show that TAPi is effective to improve the capacity retention of LiNi0.5Co0.2Mn0.3O2/Li half‐cell and LiNi0.5Co0.2Mn0.3O2/graphite full‐cell. The mechanism of TAPi is studied by a series of physical characterizations, the results indicate that TAPi forms a protective interphase film on the cathode surface after cycling. The TAPi‐derived film protects the cathode structure from destruction to improve the electrochemical performance of the LiNi0.5Co0.2Mn0.3O2 cathode at high voltage.

Insight into the solid-liquid electrolyte interphase between Li6.4La3Zr1.4Ta0.6O12 and LiPF6-based liquid electrolyte

Garnet-type Li7La3Zr2O12 (LLZO) solid electrolyte (SE) has been widely used as a promising material providing protection for Li anode in lithium-ion and hybrid-electrolyte cells due to its high ionic conductivity and superior stability against Li metal. So far much efforts have been expended on addressing the issues at LLZO/Li metal interface, but relatively little attention was placed on the interface between LLZO and liquid electrolyte (LE), while this interface is also crucial for the successful implementation of protected Li metal batteries. Herein, we devote an effort to clarifying the characteristics of the SLEI between Li6.4La3Zr1.4Ta0.6O12 (LLZTO) and LiPF6-based LE. Furthermore, the reaction mechanism and improved approaches are particularly emphasized and discussed. The presence of trace water in LE plays an important role in the formation of SLEI, as it can accelerate the H+/Li+ exchange of LLZTO and self-decomposition of LiPF6. LiF generated from LiPF6 decomposition and HF corrosion is confirmed as the main component of SLEI via X-ray photoelectron spectroscopy (XPS) depth profiling. The thickness of the SLEI increase with time, the maximum thickness is about 40 nm after immersion in LE for 48 h. We expect that this systematic methodology can serve as a reference for investigating various SLEI for broader applications.

Role of Electrolyte Oxidation and Difluorophosphoric Acid Generation in Crossover and Capacity Fade in Lithium Ion Batteries

Poor cycling performance for many high voltage lithium ion batteries (LIB) has been attributed to damage of the anode solid electrolyte interphase (SEI) resulting from crossover reactions. Transition-metal ion crossover has been proposed as a primary source of SEI damage and capacity loss, especially for high-voltage spinel cathodes. However, deposition of transition metals on the anode SEI may not be the primary source of SEI degradation. This investigation focuses on the oxidative decomposition of LiPF6 in ethylene carbonate (EC)-based carbonate electrolytes to generate acidic species which subsequently cross over to the anode and degrade the anode SEI components. The generation of the strong acid, difluorophosphoric acid (F2PO2H), has been quantified for both graphite || LiNi0.5Mn1.5O4 and graphite || LiMn2O4 cells. There is a correlation between the concentration F2PO2H, SEI degradation, and the capacity loss of the cells.

Gradient SEI layer induced by liquid alloy electrolyte additive for high rate lithium metal battery

Current energy storage device has fallen short behind from the fast growing requirement for (hybrid) electric vehicles and portable devices including mobile phones, which drives the lithium metal anode to be a research hot topic. However, the large volume change of lithium metal anode induces instable solid electrolyte interface (SEI) layer, which prevents its further development. A stable SEI layer required flexible surface to accommodate the large volume variation and inorganic core with low Li + partial molar volume for dendrite suppression. Herein, we achieved a gradient SEI which is composed of flexible surface-rich polycarbonate moieties and low Li + partial molar volume inorganic LiF-rich core by applying liquid alloy GaSnIn as electrolyte additive. Initially, the calculation verified that liquid alloy GaSnIn as electrolyte additive would facilitate the initial decomposition of LiPF 6 , and lead to the formation of the gradient SEI layer. In the Li||Li half‐cell test, we successfully achieved dense deposition of Li metal and in this way, the cycling performance with liquid alloy GaSnIn as electrolyte additive is greatly improved especially at high rate (10 mA cm −2 ). Voltage polarization was greatly reduced and Coulombic efficiency was effectively improved due to the gradient SEI layer achieved in the interface of Li anode and electrolyte. In the Li||LFP cell, high average coulombic efficiency (99.06%) at long cycle life (＞2500 cycles) is achieved for the liquid alloy GaSnIn‐protected Li metal anode at high areal capacity (3 mAh/cm 2 ). These results deepen our understanding on liquid alloy as a promising electrolyte additive for efficient dendrite suppressing, enabling the practical lithium metal batteries (LMBs). • We successfully achieved a gradient SEI layer through liquid alloy for lithium dendrite suppression. • Gradient SEI layer is composed of flexible surface-rich polycarbonate moieties and inorganic LiF-rich inside. • Liquid alloy GaSnIn as electrolyte additive facilitates the initial decomposition of LiPF6, facilitating the gradient SEI layer.

1,4-Dicyanobenzene as electrolyte additive for improve electrochemical performance of Li1.2Ni0.2Mn0.6O2 cathode materials in lithium metal rechargeable batteries

The cycling stability of Li1.2Ni0.2Mn0.6O2 cathodes is increased enormously by adding 0.1 %wt 1,4-dicyanobenzene (1,4-DCB) additive in the electrolyte, and the capacity retention increases from 20.3% to 63.8% after 350 cycles. It is found that 1,4-DCB eliminates the trace water in the electrolyte via hydrolysis under acidic conditions. A coating layer on the electrode surface is formed by preferentially oxidized of 1,4-DCB, which reduce the contact between electrolyte and cathode, inhibiting the decomposition of electrolyte solvent. N group in the electrooxidation product of 1,4-DCB can combine with PF5 to improve the stability of LiPF6, then reducing the decomposition of LiPF6. The benzene ring and conjugated bond of 1,4-DCB are favorable for the transfer of interfacial electron and ion, and then the electrochemical performance of lithium-rich layered materials is improved.

Quantifying Absolute Amounts of Electrolyte Components in Lithium-Ion Cells Using HPLC

To quantify absolute amounts of electrolyte components in lithium-ion cells, we developed a method for electrolyte extraction from pouch cells using a diluent and subsequent analysis by high-performance liquid chromatography (HPLC) coupled to an electrospray ionization mass spectrometer and an ultraviolet/visible light detector. From LiNi1/3Co1/3Mn1/3O2 (NCM111)/graphite lithium-ion pouch cells containing 1 M LiPF6 in ethylene carbonate (EC)/dimethyl carbonate (DMC) 1:1 by weight with 3 wt% vinylene carbonate (VC), electrolytes were extracted using diethyl carbonate as diluent and HPLC analyses were subsequently performed to investigate electrolyte decomposition upon electrochemical aging. Complementary analysis methods, namely X-ray photoelectron spectroscopy, gas chromatography, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and inductively coupled plasma optical emission spectrometry were applied. During formation, only VC decomposition and associated deposition of polymerized VC on the anode was identified. However, after long-term cycling, EC decomposition was dominant. Furthermore, LiPF6 decomposition and deposition of LiF on the anode were detected. Electrochemically untreated cells showed no change in electrolyte composition during storage. Unlike analyzing relative values (concentrations/quantity ratios), where only VC decomposition is detected, our approach determining absolute amounts reveals more details and allows to identify decomposition mechanisms in electrolytes upon electrochemical aging.

Suppression Mechanisms of the Solid-Electrolyte Interface Formation at the Triple-Phase Interfaces in Thin-Film Li-Ion Batteries

Side reactions of the charge/discharge in Li-ion batteries (LIBs) generate a solid-electrolyte interface (SEI) onto an electrode surface, resulting in the degradation of the lifetime of a cell. The suppression of SEI formations has attracted much attention for achieving longer cyclable LIBs. Our research group has previously reported that few SEI were observed at triple-phase interfaces (TPIs) consisting of BaTiO3, LiCoO2, and electrolyte interfaces in LIBs with excellent cyclability and ultrahigh-speed chargeability. An investigation on the suppression mechanisms of SEI formations at TPIs should yield important information on understanding the undesirable side reactions. Therefore, we have explored the suppression mechanisms of SEI formations by preparing epitaxial thin films and evaluating the surface of the samples after the electrochemical treatment. The results of X-ray photoelectron spectroscopy and scanning electron microscopy with energy-dispersive X-ray analysis measurements suggested that the decomposition of LiPF6 was suppressed at TPIs, implying that the generation of PF5 via the decomposition of LiPF6 contributed to SEI formation.

2-mercaptobenzothiazole as a surface modifier to improve the electrochemical properties of Li1.2Ni0.2Mn0.6O2 cathode materials

Li-rich layered oxides (LLO), like Li1.2Ni0.6Mn0.2O2, have certain disadvantages such as poor cycle stability and fast voltage decay. Herein, we attempt to employ simple methods, the Li1.2Ni0.2Mn0.6O2 material is modified by self-assembly of 2-mercaptobenzothiazole (MBT), to improve the electrochemical properties. The cycling stability of Li1.2Ni0.2Mn0.6O2 cathodes (LLC) is significantly increased by modified MBT, and its capacity retention increases from 52.64 to 88.47% after 125 cycles. In the meantime, the rate of medium voltage decay slows down. Lithium-deficient layer and spinel phase were formed by H+/Li+ exchange in the process of surface molecule self-assembly. In the first charge/discharge cycle, H+ in the material is removed and forms H2O molecule on the material surface, which leads to more surface spinel phase and the formation of LiF/LixPOyFz films, hereby reducing the contact between electrolyte and cathode. The phase transition and voltage decay have been suppressed by the surface spinel phase and LiF/LixPOyFz films which also improve the rate capacity. The -N=, -N+= functional groups in the modified films stabilize the PF6− and PF5, which can inhibit the decomposition of LiPF6 in the electrolyte and then reduce the content of LiF in SEI film.

Cross-Talk in Si Full-Cell with Various Cathodes

Crosstalk between cathode and anode in Li-ion batteries (LIBs) has been increasingly recognized in recent years as having a great impact on performance, safety and cycle life time. However, systemic understanding of crosstalk behavior in Si full cell with various cathode materials has not been studied. In this project, we investigated crosstalk behavior of a Si anode coupled with one of the following cathodes, LiCoO2 (LCO), LiNi0.5Mn0.3Co0.2 (NMC532), or LiFePO4 (LFP), in a full cell. For each system, we compared electrolyte decomposition products, solid electrolyte interface (SEI) chemistry, and degradation mechanisms of cells during cycling. From a very early stage of cycling, each system showed different crosstalk behavior, showing different electrolyte decomposition products and SEI chemistry on Si anodes. Especially, the SEI of the aged Si showed that decomposition of LiPF6 was more severe in the LCO/Si or the NMC532/Si cells than those containing LFP/Si. This can lead to an unstable SEI on Si anode, which can result in rapid degradation, such as significant Si pulverization and Li loss, in LCO/Si or NMC/Si system. Acknowledgment We gratefully acknowledge support from Brian Cunningham at the U. S. Department of Energy (DOE), Vehicle Technologies Office. The submitted manuscript has been created at Argonne National Laboratory. Argonne National Laboratory is operated for the DOE Office of Science by UChicago Argonne, LLC, under contract number DE-AC02-06CH11357.

Competitive Solvation Enhanced Stability of Lithium Metal Anode in Dual-Salt Electrolyte.

The development of lithium metal batteries is hindered by the low Coulombic efficiency and poor cycling stability of the metallic lithium. The introduction of consumptive LiNO3 as an additive can improve the cycling stability, but its low solubility in the carbonate electrolytes makes this strategy impractical for long-term cycling. Herein we propose LiNO3 as a cosalt in the LiPF6-LiNO3 dual-salt electrolyte to enhance the cycling stability of lithium plating/stripping. Competitions among the components and the resultant substitution of NO3- for PF6- in the solvation shell facilitate the formation of a Li3N-rich solid electrolyte interphase (SEI) film and suppress the LiPF6 decomposition. The highly Li+ conductive and stable SEI film effectively tailors the lithium nucleation, suppresses the formation of lithium dendrites, and improves the cycling performance. The competitive solvation has profound importance for the design of a complex electrolyte to meet the multiple requirements of secondary lithium batteries.

Unanticipated Mechanism of the Trimethylsilyl Motif in Electrolyte Additives on Nickel-Rich Cathodes in Lithium-Ion Batteries.

The introduction of a trimethylsilyl (TMS) motif in electrolyte additives for lithium-ion batteries is regarded as an effectual approach to remove corrosive hydrofluoric acid (HF) that structurally and compositionally damages the electrode-electrolyte interface and gives rise to transition metal dissolution from the cathode. Herein, we present that electrolyte additives with TMS moieties lead to continued capacity loss of polycrystalline (PC)-LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes coupled with graphite anodes compared to additives without TMS as the cycle progresses. Through a comparative study using electrolyte additives with and without TMS moieties, it is revealed that the TMS group is prone to react with residual lithium compounds, in particular, lithium hydroxide (LiOH) on the PC-NCM811 cathode, and the resulting TMS-OH triggers the decomposition of PF5 created by the autocatalytic decomposition of LiPF6 that generates reactive species, namely, HF and POF3. This work aims to offer a way to build favorable interface structures for Ni-rich cathodes covered with residual lithium compounds through a study to figure out the roles of TMS moieties of electrolyte additives.

Electrochemical Reactivity and Passivation of Silicon Thin-Film Electrodes in Organic Carbonate Electrolytes.

This work focuses on the mechanisms of interfacial processes at the surface of amorphous silicon thin-film electrodes in organic carbonate electrolytes to unveil the origins of the inherent nonpassivating behavior of silicon anodes in Li-ion batteries. Attenuated total reflection Fourier-transform infrared spectroscopy, X-ray absorption spectroscopy, and infrared near-field scanning optical microscopy were used to investigate the formation, evolution, and chemical composition of the surface layer formed on Si upon cycling. We found that the chemical composition and thickness of the solid/electrolyte interphase (SEI) layer continuously change during the charging/discharging cycles. This SEI layer "breathing" effect is directly related to the formation of lithium ethylene dicarbonate (LiEDC) and LiPF6 salt decomposition products during silicon lithiation and their subsequent disappearance upon delithiation. The detected appearance and disappearance of LiEDC and LiPF6 decomposition compounds in the SEI layer are directly linked with the observed interfacial instability and poor passivating behavior of the silicon anode.

2-Thiophene sulfonamide (2-TS)-contained multi-functional electrolyte matching high-voltage LiNi0.8Mn0.1Co0.1O2/graphite batteries with enhanced performances

2-thiophene sulfonamide (2-TS) is demonstrated as a multi-functional additive to functionalize the electrolyte and improve the performances of LiNi0.8Mn0.1Co0.1O2 (NCM811)/graphite batteries. Compared with the batteries without 2-TS, the performances of batteries with 2-TS containing electrolyte are significantly improved at wide temperature and high cut-off charge voltage of 4.40 V (vs. Li/Li+）. After 500 cycles at room temperature and in the voltage range of 2.80–4.20 V, the batteries with 1% 2-TS and without 2-TS additive lose 8.40% and 23.59% initial discharge capacity, respectively. At an elevated temperature of 45 °C and in the voltage range of 2.80–4.40 V, the cycle performance of the batteries with 1% 2-TS is also enhanced, i.e., 68.68% initial discharge capacity is remained after 115 cycles, while the batteries without 2-TS has already decayed to the lifespan point. It is shown that 2-TS molecules can both consume the H2O/HF residues to alleviate the decomposition of LiPF6 and preferentially react on the electrodes to form uniform and dense low-resistance films. These results demonstrate this electrolyte can effectively improve the battery performances and has promising prospects applying in high-voltage and high-nickel NCM-based batteries.

Fast Operando GCMS Gas Analysis for Monitoring Electrolyte Decomposition in Lithium Ion Batteries

Lithium Ion Batteries (LIB) find not only wide use in portable devices and consumer electronics, but also attract increasing attention in stationary energy storage and the automotive sector. In this regard, LIBs play a significant role as intermediate energy storage due to their high volumetric and gravimetric energy, high power density, and long cycle life.To achieve the required performance, the interaction of novel anode and cathode materials is of paramount interest. Particularly, the safety of cell operation must be assessed with respect to the formation of volatile and reactive species during cycling which can negatively alter cell components. Gas chromatography mass spectroscopy (GCMS) has proven to be a reliable tool for species detection. Unfortunately, conventional GC systems lack time resolution for in-situ gas analysis regarding fast processes, for example battery failure. Therefore, developing operando testing methods with improved time resolution is key to giving insight into electrolyte alterations during battery operation.Here one of them, a novel multiplex injection method is presented as a monitoring technique for gas species arising from the decomposition of conventional LIB electrolytes. The combination of the multiplexing technique and GCMS allows the analysis of fast decomposition processes by 15 fold increase of time resolution compared to conventional gas chromatography. In addition, FTIR allows online monitoring of selected vibration bands. Commercially produced pouch cells were monitored with respect to evolving gas species during battery operation under overcharge conditions. For the decomposition of LiPF6 / organic carbonate- based electrolytes alkanes, alcohols, ethers, esters, aldehydes and also derivatives that appear in the presence of hydrofluoric acid such as fluorinated alkane species, have been evaluated.The author gratefully acknowledges the FFG (Austrian Research Promotion Agency) for funding this research within project No. 858298.

Li2CO3 decomposition in Li-ion batteries induced by the electrochemical oxidation of the electrolyte and of electrolyte impurities

Layered lithium transition metal oxides are state-of-the-art cathode materials for Li-ion batteries. Nickel-rich layered oxides suffer from high surface reactivity toward ambient air. Besides hydroxides, carbonates are known to be the major surface impurities formed. While the decomposition of Li2CO3 in a battery cell has been studied extensively, the mechanistic aspects of its decomposition during cell formation/cycling are still highly controversial.The decomposition reaction of Li2CO3 in a standard Li-ion battery electrolyte is studied by on-line electrochemical mass spectrometry, employing an electrode only consisting of Li2CO3 and conductive carbon. By modifying the electrode configurations in the cell, we are able to show that the decomposition of Li2CO3 occurs as a chemical process without any direct electrochemical oxidation of the Li2CO3 particles. Their decomposition proceeds by a chemical process via protons that are formed upon anodic oxidation of the electrolyte solvent and of trace impurities in alkyl carbonate based electrolytes. By adding common impurities in Li-ion battery electrolytes as ethanol and ethylene glycol, whose electrochemical oxidation at rather low anodic potentials (≈ 3.5 V vs Li+/Li) results in the formation of protons, the onset of CO2 evolution from Li2CO3 is accordingly shifted to such low potentials. Tracing the proton-induced LiPF6 decomposition products PF5/POF3, the formation of protons can be followed quantitatively and a direct correlation with the CO2 produced by the proton-induced Li2CO3 decomposition is shown. Implications of these findings for transition metal oxide based cathode materials in Li-ion batteries are discussed based on the here found decomposition mechanism.

Regulating the composition distribution of layered SEI film on Li-ion battery anode by LiDFBOP

The so-called solid-electrolyte interface (SEI) derived from the interaction between electrolyte and electrode plays a decisive role in Li-ion battery performance. Lithium difluoro(bisoxalato) phosphate (LiDFBOP) as the derivative of LiPF6 has caused great attention among the researchers. However, the mechanism of effect for LiDFBOP salt has not yet revealed, which limits the findings for the fundamental cause of performance improvement. In this work, the effect of LiDFBOP on the mesocarbon microbead (MCMB) anode electrode has been investigated with aid of surface analysis technique, such as scanning electron microscope (SEM), X-ray photoelectron spectrum (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). On the basis of the modification with LiDFBOP, the long-term cycling and degradation resistance of Li/MCMB half cells have been achieved, which results from the preferential decomposition of LiDFBOP regulating the decomposition law of the electrolyte system. The SEI film with layer structure has different composition distribution under the obstruction of LiDFBOP of the decomposition of LiPF6. The more organic ingredients are distributed in the SEI film on the electrolyte side, which leads to low impedance and fast transportation of lithium ions. The special ingredient distribution is ascribed to the obstruction of LiDFBOP on the decomposition of LiPF6. This work signifies the research of the effect of SEI film distribution on the battery performance.

Improving Stability of LiCoO2 Cathode by Using Lithium Bis(Trifluoroborane)‐5‐Cyano‐2‐(Trifluoromethyl) Benzimidazolide as Additive

AbstractLiCoO2 is an important cathode material of commercial lithium‐ion batteries (LIBs) and therefore, improving the stability when LiCoO2 cathode is overcharged can have an immediate impact on commercial LIBs. A novel Li salt, lithium 5‐cyano‐bis(trifluoroborane)‐2‐(trifluoromethyl) benzimidazolide (Li[CBTBI]) is evidenced in this study as an effective additive for improving the electrode/electrolyte interface of LiCoO2 at high voltage operation condition. The presence of 2 % additive in commercial 1 M LiPF6/EC+DEC lead to the formation of stable interface of LiCoO2 through cycles to 4.5 V, as demonstrated in cyclic voltammetry (CV). Electrochemical impedance spectroscopy (EIS) indicates a low‐impedance of the formed interface in the presence of the additive. Cyclability test also shows an improved stability in overcharging potential window by the presence of 2 % additive. In situ diffuse reflectance infrared Fourier‐transformed spectroscopy (DRIFTS) confirms the suppression of LiPF6 decomposition, delay of onset potential of solid electrolyte interphase (SEI) formation, and thin SEI comparing to that without the additive. The possible reasons of the advantageous effect of using Li salt additives are discussed.

Effect of LiPO2F2 Electrolyte Additive on Surface Electrical Properties of LiNi0.6Co0.2Mn0.2O2 Cathode

The electrolyte additive of LiPO2F2 was injected into 18,650 Li ion battery cells composed of LiNi0.6Co0.2Mn0.2O2/graphite at 25 °C to avoid the formation of the undesirable solid electrolyte interface (SEI) layer. The potential distribution on the cathode surface was studied using electric force microscopy. The average potential distribution on the surface of the cathode in the cell where the additive LiPO2F2 was injected showed ~ 100 mV higher potential than the average potential on the surface of the cathode in the cell without the additive. X-ray photoemission spectroscopy results showed that the average potential distribution characteristics were correlated with the chemical composition of the surface reactants. These results indicate that the LiPO2F2 additive controls the formation of the SEI layer on the surface of the LiNi0.6Co0.2Mn0.2O2 cathode during the electrochemical reaction in the cell and has the decisive effect of inhibiting the decomposition of LiPF6, which is the main component of the electrolyte solution. In this study, the addition of the LiPO2F2 additive to the electrolyte improves the electrochemical performance of the Li ion battery by improving the surface potential of the cathode surface and controlling the formation of the SEI layer on the surface of the LiNi0.6Co0.2Mn0.2O2 cathode.