Lithium Difluoro Oxalate Borate Research Articles

In Situ-Initiated Poly-1,3-dioxolane Gel Electrolyte for High-Voltage Lithium Metal Batteries

To realize high-energy-density Li metal batteries at low temperatures, a new electrolyte is needed to solve the high-voltage compatibility and fast lithium-ion de-solvation process. A gel polymer electrolyte with a small-molecular-weight polymer is widely investigated by combining the merits of a solid polymer electrolyte (SPE) and liquid electrolyte (LE). Herein, we present a new gel polymer electrolyte (P-DOL) by the lithium difluoro(oxalate)borate (LiDFOB)-initiated polymerization process using 1,3-dioxolane (DOL) as a monomer solvent. The P-DOL presents excellent ionic conductivity (1.12 × 10−4 S cm−1) at −20 °C, with an oxidation potential of 4.8 V. The Li‖LiCoO2 cell stably cycled at 4.3 V under room temperature, with a discharge capacity of 130 mAh g−1 at 0.5 C and a capacity retention rate of 86.4% after 50 cycles. Moreover, a high-Ni-content LiNi0.8Co0.1Mn0.1O2 (NCM811) cell can steadily run for 120 cycles at −20 °C, with a capacity retention of 88.4%. The underlying mechanism of high-voltage compatibility originates from the dense and robust B- and F-rich cathode interface layer (CEI) formed at the cathode interface. Our report will shed light on the real application of Li metal batteries under all-climate conditions in the future.

Radical Polymer-based Positive Electrodes for Dual-Ion Batteries: Enhancing Performance with γ-Butyrolactone-based Electrolytes.

Dual-ion batteries (DIBs) represent a promising alternative for lithium ion batteries (LIBs) for various niche applications. DIBs with polymer-based active materials, here poly(2,2,6,6-tetramethylpiperidinyl-N-oxyl methacrylate) (PTMA), are of particular interest for high power applications, though they require appropriate electrolyte formulations. As the anion mobility plays a crucial role in transport kinetics, Li salts are varied using the well-dissociating solvent γ-butyrolactone (GBL). Lithium difluoro(oxalate)borate (LiDFOB) and lithium bis(oxalate)borate (LiBOB) improve cycle life in PTMA||Li metal cells compared to other Li salts and a LiPF6- and carbonate-based reference electrolyte, even at specific currents of 1.0Ag-1 (≈10C). Further, the use of LiDFOB reveals a superior rate performance, i.e., ≈90% capacity at 5.0Ag-1 (≈50C). This is attributed to faster charge-transfer/mass transport, enhanced pseudo-capacitive contributions during the de-/insertion of the anions into the PTMA electrode and to lower overpotentials at the Li metal electrode.

A crown-ether-enabled eutectic electrolyte for ultra-high temperature lithium metal batteries

Lithium metal batteries (LMBs) are generally restricted to operating below 60 °C and not suitable for high-temperature applications due to their thermally susceptible carbonate electrolytes. Deep eutectic electrolytes (DEE) with strong supramolecular interactions are a new emerging type of liquid-state ionic conductors, and here we present a novel DEE—which is composed of 18-crown-6 ether (18C6) and lithium difluoro(oxalate)borate (LiDFOB)—to extend the working temperature up to 150 °C. Via combined physiochemical and theoretical characterizations, it is identified that such high thermotolerance is a result of specific solvation structure of Li(18C6)4DFOB with multiple Li–O interactions. Moreover, our newly developed DEE triggers the formation of a B/F-rich solid electrolyte interphase, contributing to superior thermal stability and enhanced compatibility with Li-metal anodes. Consequently, Li|DEE|LiFePO4 cell exhibits great tolerance to extremely high temperatures with a capacity reversibility of 83 % after 250 cycles at 120 °C. Even at 150 °C, the cell can retain 77 % of the initial capacity (105 mAh g−1) after 100 cycles. To our knowledge, the DEE is the first liquid electrolyte for LMBs working at unprecedented high-temperature. This work opens intriguing perspectives to design novel electrolytes for demanded performance of LMBs across a wide temperature range.

In Situ Structure Modulation of Cathode‐Electrolyte Interphase for High‐Performance Potassium‐Ion Battery

AbstractManganese‐based layered oxide cathodes, particularly KxMnO2 (KMO), have shown great potential in potassium‐ion batteries (PIBs) due to their low cost, high theoretical capacities, and excellent thermal stability. However, Jahn‐Teller distortion, manganese dissolution, and interface instability of electrode/electrolyte lead to structural instability and performance decay. Here, lithium difluoro(oxalate) borate (LiDFOB) is introduced as an electrolyte additive to improve the electrochemical performance of P3‐type KMO. LiDFOB creates a uniform, thin, and robust cathode‐electrolyte interphase layer on the cathode surface, enhancing reaction kinetics, preventing manganese dissolution, and stabilizing the structure. The P3‐KMO cathode with LiDFOB in the basic electrolyte exhibits significantly improved electrochemical performance, such as a remarkable Coulombic efficiency of ≈99.5% and high capacity retention of 78.6% after 300 cycles at 100 mA g−1. Moreover, the full cell of P3‐KMO||soft carbon demonstrates satisfactory specific capacity and energy density. This study emphasizes the importance of interface chemistry for PIBs.

Insights into the multi-functional lithium difluoro(oxalate)borate additive in boosting the Li-ion reaction kinetics for Li3VO4 anodes.

The rational design of a solid electrolyte interphase (SEI) with high ionic conductivity and high electrochemical stability is significantly important in improving the electrochemical performance of anode materials. Herein, lithium difluoro(oxalate)borate (LiDFOB) is used as an electrolyte additive to generate protective SEI films on Li3VO4 (LVO) anodes. The addition of LiDFOB is beneficial to form a dense, uniform, stable and LiF-richer SEI, which is helpful to boost the Li-ion storage kinetics. In addition, the generated SEI can inhibit the further decomposition of electrolytes and maintain the morphology of LVO anodes during charge/discharge processes. As a result, LVO-based anodes exhibit a much higher capacity (769.5 mA h g-1 at 0.5 A g-1), enhanced rate performance (243.3 mA h g-1 at 5.0 A g-1) and excellent long-term cycling stability (209.9 mA h g-1 after 5000 cycles) when cycled in 1 wt% LiDFOB addition electrolyte. This work confirms that LiDFOB is a promising multi-functional additive for LiPF6 electrolytes and provides new insights into SEI construction towards high-performance LVO anodes.

Implantation of Solid Electrolyte Interphase Stabilizer within High-Capacity Silicon Electrode Enabling Enhanced Battery Performance

The commercial application of high-capacity silicon (Si) anode in lithium-ion batteries is limited by the marked volume expansion and continuous interface side reactions between the active material and the electrolyte. To address the issues, one popular strategy is to induce functional salt additives to the electrolyte, which could help to construct a robust solid electrolyte interphase (SEI) to resist the undesirable parasitic reactions and fast electrode failure. However, there exists the shortness of the dependency in the solubility of the additive salt and the possible homogeneity of the SEI. In light of this, we propose an innovative method of incorporating an SEI stabilization regent, exemplified by lithium difluorooxalate borate (LiDFOB), in the Si anode. This approach facilitates the effective utilization of the functional SEI stabilizer and impressively enhances the presence of inorganic compounds within the SEI. The resultant stable SEI effectively impedes interfacial side reactions, mitigates substantial expansion/contraction, and promotes the transport of Li + ions. As a result, the Si electrode incorporated with LiDFOB displays superior long cycle life and enhanced rate capability, indicating the advancement of planting LiDFOB in the electrode in promoting the development of advanced high-energy-density lithium-ion batteries.

Identifying lithium difluoro(oxalate)borate as a multifunctional electrolyte additive to enable high-voltage Li4Ti5O12 lithium-ion batteries

Lithium difluoro(oxalate)borate (LiDFOB) is identified as a multifunctional electrolyte additive, stabilizing the electrolyte and protecting the electrodes, to enable the LiNi0.5Mn1.5O4//Li4Ti5O12 battery with an excellent performance at 3.50 V.

(Best Poster Award - 1st Place) Characterisation of the Li Metal|Electrolyte Interface of PEO-Based SPEs with Borate Salts, Using in Situ Li Deposition PES Measurements Aided by AIMD Simulations

Lithium metal and anode-free batteries has the potential to increase the energy density and specific energy of the batteries drastically. However, when regular electrolyte materials are tried for these concepts they are plagued with problems due to degradation of the electrolyte at the interface and processes like dendrite formation which leads to poor capacity retention.[1] A strategy to mitigate these problems is to use Solid Polymer Electrolytes (SPEs), as these have better stability towards lithium metal. In order to find appropriate chemistries to use in SPE-based cells it is important to investigate and understand their anode interface, as this is where the Solid Electrolyte Interphase (SEI) is created from the degradation products during cycling.This work investigates three polyethylene oxide (PEO)-based SPEs, using lithium tetrafluoroborate (LiBF4), lithium bis(oxalate)borate (LiBOB), and lithium difluoro(oxalate)borate (LiDFOB) as the lithium conducting salts. The interfaces of these SPEs (PEO:LiBF4, PEO:LiBOB, and PEO:LiDFOB) was studied using Photo-Electron Spectroscopy (PES) with in situ lithium deposition, where lithium atoms are evaporated on top of the SPE film. The analysis of the core-level spectra before and after lithium deposition is compared to Ab Initio Molecular Dynamics (AIMD) simulations of the interface, where lithium atoms are gradually added during the simulation. These experimental and theoretical methods are meant to mimic the electrochemical plating of lithium at the lithium|SPE interface during charging of a lithium metal or anode-less cell.The interfaces of PEO:LiBOB and PEO:LiBF4 show, among other compounds, polyethylene as a breakdown product at the interface. PEO:LiDFOB shows a much lesser degree of degradation compared to the other two systems. The degradation layer is however still effective at protecting the SPE from further breakdown, as PEO:LiDFOB has a relatively high capacity retention compared to PEO:LiBF4 and PEO:LiBOB. Suggested is that the LiF provides a better electrochemical stability, while the boron and oxalate breakdown products provides a higher mechanical stability at the interface.[1] Huang WZ, Zhao CZ, Wu P, Yuan H, Feng WE, Liu ZY, Lu Y, Sun S, Fu ZH, Hu JK, Yang SJ. Anode‐Free Solid‐State Lithium Batteries: A Review. Advanced Energy Materials. 2022 Jul;12(26):2201044. Figure 1

Exploring the Efficiency of Lithium Stripping/Plating in Solid Polymer Anode-Free Lithium Cells

Traditional Li-ion batteries (LIBs) are widely used in various electronic devices due to their advantages in energy storage applications. However, finding ways to push the energy densities even higher would be highly desirable for the further rapid development of electric vehicles and electromobility. Li metal batteries and anode-free batteries (AFBs) – where the Li metal is plated in situ from Li+ ions taken from the cathode – have received extensive attention and research due to their very high specific capacity.[1] However, Li ions are unevenly deposited on the surface of anodes to form Li dendrite during the charging and discharging process, which severely deteriorates their electrochemical performance and battery safety.[2] To solve this problem, many researchers choose solid polymer electrolytes (SPEs) instead of liquid electrolytes in the batteries, because of the stability of SPEs towards Li metal.Long-term cycling of AFBs requires high-efficiency Li metal stripping and plating, which in a solid polymer cell is highly dependent on the polymer electrolyte system used, so finding appropriate host materials and salts to for the SPEs is very necessary. Poly(ethylene oxide) (PEO)-based SPEs are one of the most popular host materials for SPEs, due to their excellent chemical stability. Poly(ε-caprolactone) (PCL)-based SPEs have higher ionic conductivity and can be cycled at room temperature.[3] Poly(trimethylene carbonate) (PTMC)-based SPEs have high lithium transference number and better mechanical properties.[4] Lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) is one of the most popular salts used for SPEs. Recently, lithium difluoro(oxalate)borate (LiDFOB) and lithium bis(oxalato)borate (LiBOB) have been considered a promising alternative as electrolyte because they can passivate electrode surfaces and protect electrode materials.[5] Combinations of these materials are all potentially relvant for application in AFBs.In this work, three different polymer host materials, PEO, PTMC, and PCL, were explored as polymer electrolytes together with LiTFSI salt for their performance in anode-less cell setups, testing the plating/striping coulombic efficiency (CE) in Cu || Li cells. The results reveal clear issues for the CE of cycling in the PEO:LiTFSI system, while low-concentration PTMC:LiTFSI instead shows much more promising results. Changing the LiTFSI salt for LiBOB or LiDFOB also improves the CE of the cells.[1] Beyene, T. T., Jote, B. A., Wondimkun, Z. T., Olbassa, B. W., Huang, C. J., Thirumalraj, B., Wang C. H., Su W. N., Dai H., Hwang B. J., Effects of concentrated salt and resting protocol on solid electrolyte interface formation for improved cycle stability of anode-free lithium metal batteries, ACS applied materials & interfaces, 2019, 11(35), 31962.[2] Huang W. Z., Zhao C. Z., Wu P., Yuan H., Feng W. E., Liu Z. Y., Lu Y., Sun S., Fu Z. H., Hu J. K., Yang S. J., Anode‐Free Solid‐State Lithium Batteries: A Review, Advanced Energy Materials, 2022, 12(26), 2201044.[3] Chiu, C. Y., Chen, H. W., Kuo, S. W., Huang, C. F., Chang, F. C., Investigating the effect of miscibility on the ionic conductivity of LiClO4/PEO/PCL ternary blends. Macromolecules, 2004, 37(22), 8424.[4] Li Z., Mogensen R., Mindemark J., Bowden T., Brandell D., Tominaga Y., Ion‐conductive and thermal properties of a synergistic poly (ethylene carbonate)/poly (trimethylene carbonate) blend electrolyte. Macromolecular rapid communications, 2018, 39(14):1800146.[5] Shkrob, I. A., Zhu, Y., Marin, T. W., Abraham, D. P., Mechanistic Insight into the Protective Action of Bis (oxalato) borate and Difluoro (oxalate) borate Anions in Li-Ion Batteries, The Journal of Physical Chemistry C, 2013, 117(45), 23750.

Synergistic effect of lithium salt and trimethyl phosphate for enhanced interface stability in solid-state lithium metal batteries

Polymer electrolytes hold significant potential in solid-state battery applications due to their high flexibility and scalable manufacturing capabilities. However, it is still necessary to address the safety problems and poor rate performance. Herein, the synergistic effect of trimethyl phosphate (TMP) and lithium difluoro(oxalate)borate (LiDFOB) in the in-situ fabricated poly-butyl acrylate (PBA) quasi-solid electrolyte (QSE) is investigated. The non-flammable additive, TMP, has proven to combine with LiDFOB in the electrolytes as TMP-DFOB− pair. The TMP-DFOB− pair can promote the formation of a B–O, B–F, LiF, and Li3P containing solid electrolyte interphase (SEI) on the lithium anode, enabling stable lithium striping-plating processes. Besides, it enhances the formation of a LiF-rich cathode electrolyte interphase (CEI) and promotes intimate contact between the cathode active materials and PBA-QSE, thereby enhancing the rate performance. Therefore, the Li/PBA-LiDFOB-0.1TMP/LiFePO4 (LFP) cell delivers discharge capacity of 132 mAh g−1 with a remarkable capacity retention of 95.68 % after 500 cycles at 1 C. Even at 4 C, the discharge capacity reaches 92.1 mAh g−1. This non-flammable PBA-LiDFOB-TMP QSE exhibits potential application in high energy density systems. Furthermore, this work provides new insights into strategies for improving rate performance from lithium salts and functional additives aspects.

Endowing the Operability of Supercapacitors at High Temperatures by Regulating the Solvation Structure in Dilute Hybrid Electrolyte with Trimethyl Phosphate Cosolvent.

The redox stabilities of different oxygen donor solvents (C═O, P═O and S═O) and lithium salt anions for supercapacitors (SCs) electrolytes have been compared by calculating the frontier molecular orbital energy. Among six lithium difluoro(oxalate)borate (LiDFOB)-based mono-solvent electrolytes, the dilute LiDFOB-1,4-butyrolactone (GBL) electrolyte exhibits the highest operating voltage but suffers from electrolyte breakdown at elevated temperatures. Trimethyl phosphate (TMP) exhibits the highest redox stability and a strongly negative electrostatic potential (ESP), making it suitable for promoting the dissolution of LiDFOB as expected. Therefore, TMP is selected as a co-solvent into LiDFOB-GBL electrolyte to regulate Li+ solvation structure and improve the operability of electrolytes at high temperatures. The electrochemical stable potential window (ESPW) of 0.5m LiDFOB-G/T(5/5) hybrid electrolyte can reach 5.230 V. The activated carbon (AC)-based symmetric SC using 0.5m LiDFOB-G/T(5/5) hybrid electrolyte achieves a high energy density of 54.2Whkg-1 at 1.35kWkg-1 and the capacitance retention reaches 89.2% after 10000 cycles. The operating voltage of SC can be maintained above 2V when the temperature rises to 60°C.

Improved Sigr/NCM523 Cycling Via Triethyl Phosphate-Solubilized Lithium Nitrate Electrolyte

The performance of silicon-graphite (SiGr)/Li and SiGr/NCM523 cells were investigated in electrolytes containing lithium difluoro(oxalate)borate (LiDFOB) and lithium nitrate (LiNO3) in ethylene carbonate (EC), ethylmethyl carbonate (EMC), and different proportions of triethyl phosphate (TEP). While the LiDFOB and LiNO3-containing electrolytes both showed improved cycling stability over industry standards, the 10% TEP electrolyte demonstrated the best capacity retention in half cells and the best overall cycling performance in full cells. Ex-situ surface analysis reveals that the LiDFOB and LiNO3 preferentially decompose on both the anode and cathode surface during the first cycle to generate films consisting of oxalates, fluoroborates, and nitrate reduction products. Therefore, incorporation of two different film-forming electrolyte additives into the electrolyte is significantly more beneficial in formation of a robust SEI and improved cycle life in silicon-containing anodes.

Prospective Application, Mechanism, and Deficiency of Lithium Bis(oxalate)Borate as the Electrolyte Additive for Lithium‐Batteries

AbstractLithium bis(oxalate)borate (LiBOB) is one of the most common film‐forming electrolyte additives used in lithium ion batteries (LIBs), since it can form a dense boron‐containing polymer as a solid electrolyte interlayer (or cathode electrolyte interlayer) in order to isolate the electrode material from the electrolyte and prevent side reactions. LiBOB can serve as HF scavenger to maintain the structural integrity of electrodes via avoiding the transition metal dissolution caused by HF attack. LiBOB also can react with LiPF6 to generate lithium difluoro (oxalate)borate (LiDFOB) that can be further used as a clean‐up agent for reactive oxygen radicals. This article lists the application of LiBOB in high capacity and high voltage cathode materials, and also reviews the working mechanisms of LiBOB used in these materials to improve the performance of LIBs. Finally, it presents the current shortcomings of LiBOB and strategies to overcome these. This article is expected to provide useful insights for employing LiBOB as a feasible method of dealing with the difficulty of running high capacity LIBs stably under high voltage.

Initiator-free in-situ synthesized polymer electrolytes with high ionic conductivity for dendrite-free lithium metal batteries

In-situ preparation of polymer electrolytes (PEs) can enhance electrolyte/electrode interface contact and accommodate the current large-scale production line of lithium-ion batteries (LIBs). However, reactive initiators of in-situ PEs may lead to low capacity, increased impedance and poor cycling performance. Flammable and volatile monomers and plasticizers of in-situ PEs are potential safety risks for the batteries. Herein, we adopt lithium difluoro(oxalate)borate (LiDFOB)-initiated in-situ polymerization of solid-state non-volatile monomer 1,3,5-trioxane (TXE) to fabricate PEs (In-situ PTXE). Fluoroethylene carbonate (FEC) and methyl 2,2,2-trifluoroethyl carbonate (FEMC) with good fire retardance, high flash point, wide electrochemical window and high dielectric constant were introduced as plasticizers to improve ionic conductivity and flame retardant property of In-situ PTXE. Compared with previously reported in-situ PEs, In-situ PTXE exhibits distinct merits, including free of initiators, non-volatile precursors, high ionic conductivity of 3.76 × 10−3 S cm−1, high lithium-ion transference number of 0.76, wide electrochemical stability window (ESW) of 6.06 V, excellent electrolyte/electrode interface stability and effectively inhibition of Li dendrite growth on the lithium metal anode. The fabricated LiFePO4 (LFP)/Li batteries with In-situ PTXE achieve significantly boosted cycle stability (capacity retention rate of 90.4% after 560 cycles) and outstanding rate capability (discharge capacity of 111.7 mAh g−1 at 3C rate).

Crystallographic oriented plating by using lithiophilic ionic additives in carbonate electrolyte for enabling high voltage lithium metal batteries

The practical utilizations of high voltage (>4.0 V) lithium (Li) metal batteries are severely hindered by the unstable solid electrolyte interphase (SEI) and uncontrolled growth of dendritic Li in carbonate electrolyte. In this work, lithiophilic active ionic additives (In(NO3)3, lithium difluoro(oxalate)borate (LiDFOB), and LiNO3) are adopted to generate a multi-layer SEI in commercial carbonate electrolyte and promote the preferential Li plating along the (200) direction. As evidenced theoretically and experimentally, it is found that In(NO3)3 ionic additive generates a lithiophilic In-containing inner SEI layer, which induces the oriented Li plating along the (200) plane and a low surface energy of deposited Li. In addition, the LiDFOB additive is used to obtain LiF-rich middle SEI to improve the interfacial energy of SEI, and the LiNO3/tetramethylene sulfone (TMS) additive generates a Li3N-rich outer SEI to accelerate Li+ transport. As a result, the modified carbonate electrolyte can ensure the Li (50 μm) ‖LiNi0.8Co0.1Mn0.1O2 full cell to realize an ultra-high average CE of 99.3 % and a high-capacity retention of 94.2 % after 100 cycles. This work reveals the mechanism of multi-layer SEI induced crystallographic oriented Li plating and the internal mechanism of Li+ transport, and provides a simple approach to bring Li metal into practical high voltage Li metal batteries.

Improved Cycling of Li||NMC811 Batteries under Practical Conditions by a Localized High-Concentration Electrolyte.

Li||NMC811 battery, with lithium-metal (high specific capacity and low redox potential) as anode and LiNi0.8 Co0.1 Mn0.1 O2 (NMC811) as cathode, has been widely accepted to be a good candidate as one of the high-energy-density batteries. However, its cyclability needs improvement to fulfill the requirement for its future commercial use, especially under practical conditions. Electrolyte plays a key role in improving the cycling performance of Li||NMC811 batteries, where a high voltage/electrochemical window and good stability with the electrodes of the electrolyte are required. Herein, a localized high-concentration electrolyte with an additive of lithium difluoro(oxalate)borate (LiDFOB) is reported that improves the cycling performance of Li||NMC811 cells under crucial conditions with Li foil thickness of 50µm, cathode areal loading of 4mAhcm-2 , the areal capacity ratio between the negative and positive electrodes (N/P ratio)of 2.6 and the electrolyte/cell capacity ratio (E/C ratio) of 3.0g(Ah)-1 . These cells can maintain 80% of the capacity after 195 cycles.

An additive-enabled ether-based electrolyte to realize stable cycling of high-voltage anode-free lithium metal batteries

To achieve stable cycling of high-energy-density and high-voltage anode-free lithium metal batteries, the interfacial stability of both lithium metal anode and high-voltage cathode is demanded. Electrolytes based on ether solvents tend to have excellent compatibility with the lithium metal anode, but due to their low oxidation potential (generally less than 4.0 V vs. Li+/Li), they render high-voltage LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes unsatisfactory electrochemical performance. Here, an average Coulombic efficiency of 99.4% is realized for lithium metal plating-striping by using an ether-based local high-concentration electrolyte. By further introducing a minute amount of lithium difluoro(oxalate)borate (LiDFOB) additive (0.02 M) into this baseline electrolyte, its oxidation stability is increased to 4.3 V without compromising its high Coulombic efficiency towards reversible lithium plating-striping. Consequently, this additive-supported electrolyte enables the high-loading (3.0 mAh cm−2) Cu||NCM811 anode-free cells to achieve high-capacity retention at both room temperature (∼95% capacity retention after 50 cycles) and -20 ˚C (∼79% capacity retention after 30 cycles). A combination of microscopic and spectroscopic investigations aided by theoretical calculations demonstrate that the LiDFOB additive helps generate a Li3N- and LiF-rich solid electrolyte interphase on the lithium metal anode side, enabling dense and uniform lithium deposition, meanwhile, it also leads to a uniform and compact cathode electrolyte interphase on the high-voltage NCM811 cathode side, mitigating the transition metals dissolution. This work provides a simple and promising strategy for the electrolyte design of high-voltage anode-free batteries.

Lithium Difluoro(Oxalate)Borate‐Induced Interphase for High‐Voltage LiFe0.15Co0.85PO4@C Cathode by Solid‐State Synthesis

Herein, the effect of lithium difluoro(oxalate)borate (LiDFOB) as an electrolyte additive on the electrochemical performance of LiFe0.15Co0.85PO4@C (LFCP@C) cathode, synthesized by a scalable solid‐state synthesis method is reported. Galvanostatic studies revealed better electrochemical performance among the LFCP@C (LiDFOB: 0.5–2 wt%) in a half‐cell assembly compared to the LiFe0.15Co0.85PO4 in the absence of LiDFOB. Also, among the various concentrations of LiDFOB, the LFCP@C (LiDFOB—1.5 wt%) and LFCP@C (LiDFOB—2 wt%) are optimized as suitable candidates for further electrochemical studies owing to the high discharge capacities of 116 and 118 mAh g−1. In addition, the electrochemical impedance studies (EIS) exhibited an increase in the charge–transfer resistance (R ct) as the amount of LiDFOB was increased, whereas a lower R ct value is observed in the absence of additive. In addition, the diffusion coefficient calculation is calculated using the EIS data, which shows a diffusion coefficient in the order of ≈10−13 cm2 s−1. However, as the amount of LiDFOB is increased from 0 to 2 wt%, a decrease in the diffusion coefficient is observed owing to the formation of a stable and thicker passivation layer.

Cyclability improvement of high voltage lithium cobalt oxide/graphite battery by use of lithium difluoro(oxalate)borate electrolyte additive

In order to overcome severe capacity fading of LiCoO2/graphite lithium-ion battery at a high voltage, lithium difluoro(oxalate)borate (LiDFOB) was investigated as an electrolyte additive. Electrochemical tests demonstrate that by adding 1 wt.% LiDFOB into a carbonate electrolyte, the capacity retention of the battery after 300 cycles at 1 C between 3.0 and 4.5 V is improved from 42.1 to 80.2%. With the help of computational calculations and physical characterization techniques, we found that the LiDFOB strongly coordinates with Co ions, which inhibits the dissolution of cobalt from bulk LiCoO2 and prevents Co deposition on the anode. Meanwhile, the LiDFOB additive form stable, uniform, and thin surface films simultaneously on positive and negative of the LiCoO2/graphite battery, inhibiting the electrolyte decomposition and leading to the improvement of the batteries performance.

A fluorinated electrolyte stabilizing high-voltage graphite/NCM811 batteries with an inorganic-rich electrode-electrolyte interface

Increasing the operating voltage of Ni-rich cathode materials is a promising route to achieve lithium-ion batteries with a high energy density. However, the unstable electrode–electrolyte interface (EEI) caused by the decomposition of carbonate-based electrolytes at high voltage is a major obstacle. Herein, it is reported that the superior electrochemical performance of the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode at 4.6 V is achievable using a novel electrolyte system containing fluorinated carbonate and fluorinated carboxylate with a lithium difluoro(oxalate)borate (LiDFOB) additive. The stable B- and F-rich inorganic EEI at high voltage can reduce electrochemical polarization while also preventing the collapse of the cathode structure and continuous dissolution of transition metal ions. As a result, our designed fluorinated electrolyte enables Li/NCM811 half-cells to deliver a high specific capacity (247.2 mAh g−1), superior cyclability (81.4% retention at 200 cycles, 0.5C) and rate performance (154.5 mAh g−1 at 5C) at 4.6 V. The designed electrolyte also enables graphite (Gr)/NCM811 full cells with high loading cathode (≈ 9.5 mg cm−2) to achieve a high capacity retention of 83.3% (0.5C) after 100 cycles at 4.6 V. This work provides a new method to achieve high energy density Gr/NCM811 batteries at high voltage.