Dissolution Of Transition Metal Ions Research Articles

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.

Mn2+ Ions Capture and Uniform Composite Electrodes with PEI Aqueous Binder for Advanced LiMn2O4-Based Battery.

The electrode deterioration and capacity decay caused by the dissolution of transition metal ions have been criticized for a long time. The branched polyethyleneimine (PEI) was employed as a functional binder for spinel lithium manganese oxide (LiMn2O4, LMO) and layer structure lithium cobalt oxide (LiCoO2, LCO) to resolve the problem. Due to the chelation reaction of amine groups, PEI polymer binder can effectively absorb soluble transition metal ions, which is beneficial to reduce the loss of active materials. For PEI-based cathode, the uniform distribution of key components is achieved by the rapid curing process of water, which endow PEI-based cathode with a higher Li+ diffusion coefficient and improved electrochemical reaction kinetics. In addition, the fixed binder coating is favorable to protecting the active materials from parasitic reaction with the lithium hexafluorophosphate (LiPF6)-based electrolyte. Therefore, the PEI-based cell shows superior rate capability and long-term cycle performance. Functional binders of this study provide a simple and effective strategy to achieve higher capacity and longer cycle stability for transition metal oxide electrodes.

Insights into the Crossover Effects in Cells with High‐Nickel Layered Oxide Cathodes and Silicon/Graphite Composite Anodes

AbstractSilicon anodes are regarded as one of the most promising alternatives to graphite (Gr) anodes due to their ultrahigh capacity, abundance, and low cost. Coupling Si‐based anodes with high‐nickel layered oxide cathodes LiNixMnyCo1−x−yO2 (NMC, x ≥ 0.8) can enhance the driving range for electric vehicles. Transition‐metal (TM) ion dissolution and deposition has been a long‐known failure mode for Gr‐based lithium‐ion batteries. However, the mechanistic insight associated with TM ion deposition on Si‐based anodes has rarely been reported. Herein, the impact of in situ deposited TM ions on SiOx/Gr composite anodes and the individual influences of Ni, Mn, and Co on the structural and electrochemical stability along with the underlying degradation mechanisms are presented. TM ion dissolution causes a greater deleterious impact on Si than on Gr, with different TM ions exhibiting different influences on anode‐electrolyte interphase formation. Specifically, Ni deposit induces more aggressive salt decomposition; Co deposit has negligible effect on salt decomposition, but significantly accelerates solvent decomposition; and Mn deposit aggravates both salt and solvent decompositions, resulting in worse full cell performance. The extent of degradation decreases in the order Mn2+ > Ni2+ > Co2+. The systematic comparisons presented can guide further development of high energy systems.

Nonflammable quasi-solid electrolyte for energy-dense and long-cycling lithium metal batteries with high-voltage Ni-rich layered cathodes

Nonflammable quasi-solid electrolyte is prepared by copolymerizing flexible chains of polymer vinyl acetate and rigid skeletons of triethylene glycol diacrylate with assistance of flame-retardant phosphate solvents. The quasi-solid electrolyte simultaneously features a high conductivity (1.02 mS cm−1), a high Li+ transference number (0.65), a wide electrochemical window (5.2 V vs. Li+/Li) and rigid-flexible coupling characteristics. Moreover, the electrolyte can capture the phosphate solvents with polar molecular interactions to weaken Li+–solvent interactions while promoting Li+–anion interactions, which creates more anion-derived protective layer on both electrodes. Thus, the electrolyte not only suppresses side reactions, irreversible phase transition, stress-corrosion cracking, and the dissolution of transition-metal ions on the cathode side, but also enables highly reversible Li metal stripping/plating, leading to low pulverization on the anode side. Employing the quasi-solid electrolyte, our LiNi0.8Co0.1Mn0.1O2||Li battery increases the upper cut-off voltage from current 4.3 V to 4.5 V (versus Li+/Li), therefore, delivers an ultrahigh specific capacity of > 224.7 mAh g−1, average Coulombic efficiency of > 99.6% and capacity retention of ∼81.2% over 500 cycles.

3-(Trifluoromethyl)benzoylacetonitrile: A multi-functional safe electrolyte additive for LiNi0.8Co0.1Mn0.1O2 cathode of high voltage lithium-ion battery

The high nickel layered oxide cathode LiNi0.8Co0.1Mn0.1O2 (NCM811) is widely used in new energy power and equipment due to its high density and low cost. However, the NCM811 cathode is prone to structural rupture, dissolution of transition metal ions, and damage to the electrode/electrolyte interface under high voltage, causing degradation of battery performance and safety issues. In this paper, 3-(Trifluoromethyl)benzoylacetonitrile (3-TBL) was selected as a film-forming flame-retardant additive for the NCM811 cathode of the high-voltage lithium-ion battery, and the synergistic effect with lithium difluoro(oxalato)borate enhanced the battery cycle and safety performance. The results show that: 3-TBL is oxidized preferentially more than carbonate solvent to form a stable and dense cathode-electrolyte interface film, which effectively prevents the continuous oxidative decomposition of the electrolyte and enhances the rate of cycling and overcharge resistance of the Li/NCM811 cells under high pressure. Furthermore, the 3-TBL modified electrolyte can also delay the thermal decomposition temperature of the commercial electrolyte and improve its flame retardant properties. Kinetic analysis showed that the additive increased the activation energy required for the thermal decomposition reaction of electrolyte and NCM811 cathode mixture. Therefore, the additives 3-TBL improve the intrinsic safety of the electrolyte and electrolyte interface, providing a feasible idea for the development of high energy density and high safety electrolytes.

Study on low-temperature cycle failure mechanism of a ternary lithium ion battery.

This study is focused on the changes in parameters such as discharge capacity, and the possible failure mechanism of a 25 Ah ternary lithium ion battery during cycling at −10 °C. A new battery and a battery after 500 cycles were disassembled. The morphology and structure of the cathode and anode electrodes were characterized. Transmission electron microscopy (TEM) and X-ray photoelectron absorption spectroscopy (XPS) were used to analyze the changes in the microstructure and chemical environment of the anode electrode interface. The results show that after 500 cycles at −10 °C, the capacity of the battery is only 18.3 Ah, and there is a large irreversible capacity loss. The battery samples after low-temperature cycling produced gas during storage at 25 °C. It is found that a large amount of lithium plating on the anode surface is an important factor for the reduction in battery capacity. The dissolution of transition metal elements in the cathode electrode and deposition on the anode electrode, and the catalytic decomposition of electrolyte at the anode interface are the main reasons for the gassing of the battery.

Exploring the Solvation Sphere and Spatial Accumulation of Dissolved Transition-Metal Ions in Batteries: A Case Study of Vanadyl Ions Released from V2O5Cathodes

Dissolution of transition-metal ions from Li-ion battery cathodes is a well-known degradation phenomenon. In addition to capacity decrease due to metal loss in the bulk cathode, dissolved transition-metal ions might migrate through the electrolyte and participate in redox reactions resulting in electrolyte decomposition. Aside from the oxidation state and concentration of the transition metal, its ligand sphere and spatial accumulation have to be determined for complete characterization and prediction of possible detrimental impact. Here, pulse electron paramagnetic resonance and density functional theory are exploited to investigate the coordination and location of vanadyl ions, which are a dissolution product of V2O5 cathodes. The solvation sphere is found to be dominated by electrolyte degradation products and also contains contributions from nonelectrolytic sources. Additionally, adjacent lithium and hexafluorophosphate ions are observed.

Limitations of Ultrathin Al2O3 Coatings on LNMO Cathodes.

This study demonstrates the application of Al2O3 coatings for the high-voltage cathode material LiNi0.5–xMn1.5+xO4−δ (LNMO) by atomic layer deposition. The ultrathin and uniform coatings (0.6–1.7 nm) were deposited on LNMO particles and characterized by scanning transmission electron microscopy, inductively coupled plasma mass spectrometry, and X-ray photoelectron spectroscopy. Galvanostatic charge discharge cycling in half cells revealed, in contrast to many published studies, that even coatings of a thickness of 1 nm were detrimental to the cycling performance of LNMO. The complete coverage of the LNMO particles by the Al2O3 coating can form a Li-ion diffusion barrier, which leads to high overpotentials and reduced reversible capacity. Several reports on Al2O3-coated LNMO using alternative coating methods, which would lead to a less homogeneous coating, revealed the superior electrochemical properties of the Al2O3-coated LNMO, suggesting that complete coverage of the particles might in fact be a disadvantage. We show that transition metal ion dissolution during prolonged cycling at 50 °C is not hindered by the coating, resulting in Ni and Mn deposits on the Li counter electrode. The Al2O3-coated LNMO particles showed severe signs of pitting dissolution, which may be attributed to HF attack caused by side reactions between the electrolyte and the Al2O3 coating, which can lead to additional HF formation. The pitting dissolution was most severe for the thickest coating (1.7 nm). The uniform coating coverage may lead to non-uniform conduction paths for Li, where the active sites are more susceptible to HF attack. Few benefits of applications of very thin, uniform, and amorphous Al2O3 coatings could thus be verified, and the coating is not offering long-term protection from HF attack.

High-Performance LiNi0.8Mn0.1Co0.1O2 Cathodes By Atomic-Layer-Deposited Sulfide Coatings

Due to its higher capacity compared to the commercialized LiNixMnyCo1-x-yO2 (NMCs, 0< x, y <1) with lower Ni content (x≤0.6), LiNi0.8Mn0.1Co0.1O2 (NMC811) is now considered as the next promising cathode for lithium-ion batteries (LIBs). However, it still suffers from more serious performance degradation and safety hazard than the commercial ones. These existing issues are reflected as cation mixing, oxygen evolution, irreversible phase-transition, transition metal ion dissolution, and microcracking. Aimed at addressing these problems, surface coating has proven to be an important and effective approach. In recent years, atomic layer deposition (ALD) has emerged as an accurate tool to apply uniform and conformal coatings over NMCs at the atomic level, which have shown remarkable effects on the improved performance of batteries.1-4 Herein, for the first time we deposited ultrathin ALD Li2S coatings5 conformally over NMC811 composite electrodes. It was found that the ALD Li2S coatings enable to enhance performance of NMC811 cathodes with much better cyclability and rate capability. To clarify the effects of the ALD Li2S coatings, we utilized a suite of characterization tools including X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, and transmission X-ray microscopy. The results revealed that the ALD Li2S coatings can perfectly maintain the NMC structure during cycling, thus significantly suppress the crack formation. Furthermore, the Li2S layer can react with and eliminate H2O in electrolyte and O2 released from the NMC structure. In addition, the measurements of electrochemical impedance spectroscopy were applied, which confirms that the Li2S coatings serve as physical protection layers to prevent the interfacial reactions between the NMC cathode and liquid electrolyte. It can be foreseen that sulfides would be a new class of coating materials for addressing issues of NMC cathodes.1. Meng, X.; Yang, X. Q.; Sun, X. L., Advanced Materials 2012, 24 (27), 3589-3615.2. Liu, Y.; Wang, X.; Cai, J.; Han, X.; Geng, D.; Li, J.; Meng, X., Journal of Materials Science & Technology 2020, 54, 77-86.3. Wang, X.; Cai, J.; Liu, Y.; Han, X.; Ren, Y.; Li, J.; Liu, Y.; Meng, X., Nanotechnology 2020, 32 (11), 115401.4. Gao, H.; Cai, J.; Xu, G.-L.; Li, L.; Ren, Y.; Meng, X.; Amine, K.; Chen, Z., Chem. Mater. 2019, 31 (8), 2723-2730.5. Meng, X.; Comstock, D. J.; Fister, T. T.; Elam, J. W., ACS Nano 2014, 8 (10), 10963-10972.

Effect of Additives on the Interfacial Degradation Phenomena of LiNi0.5Mn1.5O4 Thin-Film Electrodes

LiNi0.5Mn1.5O4 shows promise as a positive electrode material for lithium-ion batteries. However, because the material has a higher operating potential than conventional cathodes, interfacial side reactions are accelerated during cycling, which degrades the outmost surface of the material. Although it has been reported that some additives offer effective protection against degradation, their protection mechanism has not been clarified in detail. Here, the effect of additives on the surface states of LiNi0.5Mn1.5O4 was investigated using thin film model electrodes. It was found that surface film was not formed on LiNi0.5Mn1.5O4 in additive-free electrolyte solution even after cycling at 55 °C, and severe dissolution of transition metal ions continuously occurred, leading to rapid capacity fading. Addition of ethylene glycol bis(propionitrile) ether (EGBE) effectively suppressed the capacity fading at 55 °C. Analysis with redox reaction of ferrocene on the electrodes, X-ray photoelectron spectroscopy, and scanning electron microscopy indicated that surface film hardly formed in EGBE-containing solution, but the dissolution was effectively suppressed. Because a nitrile group tends to adsorb on positive active material at high potential, it was concluded that the adsorption layer of EGBE impeded side reactions at the interface, resulting in improved cycleability of LiNi0.5Mn1.5O4.

Performance Degradation of Lithium‐Ion Batteries with LiNi0.33Co0.33Mn0.33O2 Cathodes during Long‐Term, High‐Temperature Storage: Behaviors and Mechanism

AbstractThe behaviors and mechanism for the different performance degradation trends of 18650 cylindrical lithium‐ion batteries (LIBs) with LiNi0.33Co0.33Mn0.33O2 cathodes under long‐term storage at a high temperature (HT) of 80 °C are investigated to gain insight on the safe use of LIBs. It is indicated that the direct current resistance (DCR) increases sharply within 240 h and then slows down gradually, whereas the open‐circuit voltage (OCV) and the recoverable capacity (RC) fading are relatively stable in the initial 240 h, but then speeds up from 240 h to 720 h. With the aid of analyses of the anode, cathode, and separator materials in batteries stored at 80 °C for 0 h, 240 h, 480 h, and 720 h, the mechanism of the performance degradation of batteries is elucidated. It is pointed out that the DCR rise is mainly caused by the anode materials peeling off from the copper foil, as is the subsequent interface resistance increase. The RC fading is attributed to the partial break of the cathode structure, owing to the dissolution of transition metal ions (Ni2+, Co3+, and Mn4+), and the dissolution becomes more severe as the time extends. In addition, the separator suffers a combination of stretching (machine direction), squeezing (anode side), oxidation (cathode side), and destruction, resulting in internal short circuit and sharp OCV drop, as well as the other potential safety risks of LIBs. These results are valuable to establish an accelerated testing method to evaluate batteries in a short time range to advance the safe use of LIBs under high‐temperature storage.

Studying the Effect of Ca Doping and Li3PO4 Coating on Ni-Rich LiNi0.91Co0.06Mn0.03O2 Ncm Cathode Material for Lithium Ion Batteries

Both environmental and energy concerns have shifted our dependence from fossil fuels to develop advanced renewable energy resources and energy storage devices for the portable electronic devices and electric vehicles [1]. Improvements in energy density, cost and safety are prime requirement for enabling the long range electrical vehicles [1]. Lithium ion batteries got huge attention due to their high discharge capacity and excellent capacity retention. Currently, Li[NixCoyMnz]O2 (NCM) is a promising candidate which has shown great potential in hybrid vehicles and electric vehicles. NCM is consists on three transition metals; Ni provides high discharge capacity but suffers from thermal instability, Co offers better electronic conductivity but at high cost and Mn provides stabilizes the host structure and enhance cycling at the cost of low capacity. Ni-rich LiNi1-x-yCoxMnyO2 (x + y ≤ 0.4 ) cathode materials have garnered a lot of attention for EV applications due to their higher discharge capacity and power density [2]. However, the major problem of Ni-rich NCM is their structural instability which leads to phase transition from layered to spinel to rock-salt structure. Another major issue is the cation mixing; unstable Ni3+ reduce to Ni2+ (0.69 Å) spontaneously, which migrates from transition metal slab (TM-slab) to Lithium slab (Li+; 0.76 Å) due to similarity in their ionic sizes. The dissolution of transition metal ions in the electrolyte (LiPF6-based) is another critical problem [3].To solve these problems, we exploit CaHPO4 to provide enhance structural stability and protects the surface from side reaction with electrolyte as well. The precursor Ni0.91Co0.06Mn0.03(OH)2 and LiOH were mixed in 1:1.05 ratio and pre-heated at 500 °C - 5 h followed by sintering at 740 °C - 15 h. The modified samples were prepared by mixing Ni0.91Co0.06Mn0.03(OH)2 and LiOH (1:1.05) along with CaHPO4 (0, 0.5, 1, 3 and 5 wt%). The samples were investigated with XRD and SEM. Later on, the electrodes were fabricated and their electrochemical properties were measured.XRD results confirm the Ca doping by shifting of (003) diffraction peak to the low angle and additional peaks were detected which belongs to the Li3PO4 phase. SEM results show that the particles have sustained their spherical morphology which means that calcium is doped successfully. The 0.5 wt% sample resulted in improved electrochemical studies as compared to the rest. The enhanced properties are originated from optimized amount of doping and coating which results in stabilizing the host structure and protecting the surface.Ca2+ enhanced the structural stability while Li3PO4 acts as Li-reactive coating to suppress the reaction between the active material and electrolyte. The modified sample offers superior cyclability and enhanced electrochemical performance.

Investigation of a Novel Bi-Functional Additive for High Voltage LiNi1.5Mn0.5O4/Graphite Cells

LiNi1.5Mn0.5O4 (LNMO)/graphite (Gr) cells are a promising candidate for commercial Li-ion batteries due to their high power density and low costs. However, the most challenging obstacle of LNMO/Gr cell is severe capacity fading at high temperature.1 The severe cell failure is associated with transition metal ion dissolution (Ni and Mn) from the positive electrode caused by acidic species, such as hydrogen fluoride, which is generated through the hydrolysis of lithium hexafluorophosphate by residual water in the electrolyte solution.2 The dissolved metal ions migrate through the electrolyte solution and deposit at the anode, where they cause a continuing deterioration and reformation of the solid electrolyte interphase,which results in an increasedcell resistance and steadily decreasing capacity utilization.To suppress these issues, a novel bi-functional electrolyte solution additive has been synthesized and tested. LNMO/Gr cells containing the additive display a significantly improved capacity retention during high temperature cycling. The end-of-test of the harvested electrodes analysis indicates that the additive may act as HF scavenger and as film-forming agent on the graphite electrode. Experiments The 2032-type coin cells were fabricated with LNMO, graphite, separators (Celgard 2325, GF/D), and electrolytes. The standard electrolyte formulation is 1.2 M LiPF6 EC:PC:DEC=15:20:65 (v/v/v). The cells were pre-cycled five times at room temperature, followed by cycled seven times for the rate testing. And then, the cells were cycled for 100 cycles at 3.3-4.9V with a rate of 1 C at 45 ℃. Constant voltage steps were applied at the end of charge with 0.05 C cut-off. Reference D. Lu, M. Xu, L. Zhou, A. Garsuch, and B. L. Lucht, J. Electrochem. Soc., 160, A3138–A3143 (2013).N. P. W. Pieczonka, Z. Liu, P. Lu, K. L. Olson, J. Moote, B. R. Powell, J. Kim, J. Phys. Chem. C, 117, 15947–15957 (2013). Figure 1 (a) The discharge capacity and (b) capacity retention of LNMO/Gr cells at 45oC. Figure 1

Enhanced High-Temperature Stability of Li-Ion Battery with Li-Rich Oxide Cathode By Localized High-Concentration Electrolyte

Lithium (Li)-rich manganese (Mn)-rich oxides (LMR) have been considered as feasible cathode materials for high-energy lithium ion batteries because they possess high theoretical specific energy over 900 Wh kg−1. However, the undesirable cathode/electrolyte interfacial reaction due to the high working voltages, which results in electrolyte decomposition, transition-metal ion dissolution and surface corrosion, is considered one of the obstacles that significantly prevent their applications in electric vehicles for years.[1, 2] Although numerous efforts have been devoted to address the surface stability issues on LMR, most of them were limited to room temperature. The continuous upsurge in demand for electric vehicles requires lithium ion batteries to be operated under elevated temperatures. While, the state-of-the-art LiPF6-organocarbonate electrolytes are not compatible with LMR cathode due to the high operating voltage, which also get worse at elevated temperatures.[3] Here, an optimized localized high-concentration electrolyte (LHCEs) is studied in graphite (Gr)-based LMR full cells at 25, 45 and 60 °C. The cycling stabilities and the interfacial properties on the surfaces of both cathode and anode under different temperatures are systemically investigated. It is revealed that the LHCE enables the formation of more protective electrode/electrolyte interphases on both anode and cathode, which, in turn, lead to significantly improved cycling stability and enhanced rate capability under the selected temperatures. The electrode/electrolyte interphases formed in LHCE are found to be less susceptible towards elevated temperatures than those in conventional LiPF6-based electrolyte. The mechanistic understanding on the function of the LHCE in Gr||LMR cells under high temperatures provides valuable perspectives of electrolyte development for practical application of LMR cathodes in high energy density batteries over a wide temperature range. References C. Wang, et al., Overlooked electrolyte destabilization by manganese (II) in lithium-ion batteries. Nature Communications, 2019, 10(1), 3423.H. Pan, et al., Li- and Mn-rich layered oxide cathode materials for lithium-ion batteries: a review from fundamentals to research progress and applications, Molecular Systems Design & Engineering, 2018, 3(5), 748.M.-T.F., Rodrigues, et al., A materials perspective on Li-ion batteries at extreme temperatures, Nature Energy, 2017, 2(8), 17108.

Recent advances in Ni-rich layered oxide particle materials for lithium-ion batteries

Ni-rich layered oxides with chemical formula of LiNixCoyMnzO2 or LiNixCoyAlzO2 (x+y+z=1, x≥0.6) have been considered as promising cathode materials for lithium-ion batteries (LIBs) because of their high specific capacity (≥180mAhg–1) and acceptable manufacture cost. However, the problems associated with high Ni content severely restrict their large-scale applications. In this review, we summarize the recent advances in Ni-rich layered oxide particle materials for LIBs. We begin with the introduction of the structure, redox mechanism, and problems of Ni-rich layered oxides, mainly including residual lithium compounds, gas evolution, rock-salt phase formation, microcrack of particles, dissolution of transition-metal ions, and thermal runaway. Then, four strategies (primary particle engineering, surface coating, doping, concentration gradient design) toward solving the problems of Ni-rich layered oxides will be systematically discussed with the emphasis on structure-performance relationships. To achieve satisfied comprehensive performance and accelerate large-scale applications of Ni-rich layered oxides, the combination of two or more strategies (particle engineering and surface/bulk stabilization techniques) with synergistic effects is necessary in future works. This review would promote further research and application of high-performance Ni-rich layered oxide particle materials for LIBs.

Inhibition of transition metals dissolution in cobalt-free cathode with ultrathin robust interphase in concentrated electrolyte

The low Coulombic efficiency during cycling hinders the application of Cobalt-free lithium-rich materials in lithium-ion batteries. Here we demonstrated that the dissolution of iron, rather than traditionally acknowledged manganese, is mainly responsible for the low Coulombic efficiency of the iron-substituted cobalt-free lithium-rich material. Besides, we presented an approach to inhibit the dissolution of transition metal ions by using concentrated electrolytes. We found that the cathode electrolyte interphase (CEI) layer formed in the concentrated electrolyte is a uniform and robust LiF-rich CEI, which is a sharp contrast with the uneven and fragile organic-rich CEI formed in the dilute electrolyte. The LiF-rich CEI not only effectively inhibits the dissolution of TMs but also stabilizes the cathode structure. The Coulombic efficiency, cycling stability, rate performance, and safety of the Fe-substituted cobalt-free lithium-rich cathode material in the concentrated electrolyte have been improved tremendously.

Protective electrode/electrolyte interphases for high energy lithium-ion batteries with p-toluenesulfonyl fluoride electrolyte additive

Abstract High energy density lithium-ion batteries using Ni-rich cathode (such as LiNi0.6Co0.2Mn0.2O2) suffer from severe capacity decay. P-toluenesulfonyl fluoride (pTSF) has been investigated as a novel film-forming electrolyte additive to enhance the cycling performances of graphite/LiNi0.6Co0.2Mn0.2O2 pouch cell. In comparison with the baseline electrolyte, a small dose of pTSF can significantly improve the cyclic stability of the cell. Theoretical calculations together with experimental results indicate that pTSF would be oxidized and reduced to construct protective interphase film on the surfaces of LiNi0.6Co0.2Mn0.2O2 cathode and graphite anode, respectively. These S-containing surface films derived from pTSF effectively mitigate the decomposition of electrolyte, reduce the interphasial impedance, as well as prevent the dissolution of transition metal ions from Ni-rich cathode upon cycling at high voltage. This finding is beneficial for the practical application of high energy density graphite/ LiNi0.6Co0.2Mn0.2O2 cells.

Aminoalkyldisiloxane as effective electrolyte additive for improving high temperature cycle life of nickel-rich LiNi0.6Co0.2Mn0.2O2/graphite batteries

A novel aminoakyldisiloxane compound, (3-(N,N-dimethylamino)diethoxypropyl) pentamethyldisiloxane (DSON), is reported as an effective electrolyte additive for improving the electrochemical performances of high energy density power batteries of nickel-rich LiNi0.6Co0.2Mn0.2O2 (NCM622)/graphite. The NCM622/graphite cells using DSON addition in the carbonate-based reference electrolyte exhibit enhanced electrochemical performances, especially high temperature performances including long cycle life and high temperature storage. The pouch cell (1 Ah) with 0.2 wt% DSON retained a capacity of 88% as compared with 84% for that without DSON in electrolyte after 200 cycles at 45 °C. The mechanism investigation reveals that DSON acts as a film-forming additive for constructing uniform conductive cathode electrolyte interphase (CEI) layer upon NCM622 particles, which suppresses the internal cracks and prohibits the irreversible phase transformation of NCM622. DSON also serves as an effective water/acid scavenger and inhibits the hydrolysis of LiPF6, thus effectively blocking the occurrence of side reactions and the dissolution of transition metal ions from cathode. Therefore, NCM622 cathode sheet maintains a better integrity surface morphology after 100 cycles. This work demonstrates that aminoakyldisiloxane is promising for practical use as effective electrolyte additive for high energy density power batteries of nickel-rich NCM/graphite.

Armoring LiNi1/3Co1/3Mn1/3O2 Cathode with Reliable Fluorinated Organic–Inorganic Hybrid Interphase Layer toward Durable High Rate Battery

AbstractTernary layered oxide materials have attracted extensive attention as a promising cathode candidate for high‐energy‐density lithium‐ion batteries. However, the undesirable electrochemical degradation at the electrode–electrolyte interface definitively shortens the battery service life. An effective and viable approach is proposed for improving the cycling stability of the LiNi1/3Co1/3Mn1/3O2 cathode using lithium difluorophosphate (LiPO2F2) paired with fuoroethylene carbonate (FEC) as co‐additives into conventional electrolytes. It is found that the co‐additives can greatly reduce the interface charge transfer impedance and significantly extend the life span of LiNi1/3Co1/3Mn1/3O2//Li (NMC//Li) batteries. The developed cathode demonstrates exceptional capacity retention of 88.7% and remains structural integrity at a high current of 5C after 500 cycles. Fundamental mechanism study indicates a dense, stable fluorinated organic–inorganic hybrid cathode‐electrolyte interphase (CEI) film derived from LiPO2F2 in conjunction with FEC additives on the surface of NMC cathode material, which significantly suppresses the decomposition of electrolyte and mitigates the dissolution of transition metal ions. The interfacial engineering of the electrode materials stabilized by the additives manipulation provides valuable guidance for the development of advanced cathode materials.

Mechanism Study of Unsaturated Tripropargyl Phosphate as an Efficient Electrolyte Additive Forming Multifunctional Interphases in Lithium Ion and Lithium Metal Batteries.

Electrolytes in modern Li ion batteries (LIBs) rely on additives of various structures to generate key interphasial chemistries needed for desired performances, although how these additives operate in battery environments remains little understood. Meanwhile, these traditional additives face increasing challenges from emerging battery chemistries, especially those based on the nickel cathode (Ni ≥ 50%) or the metallic lithium anode. In this work, we report a new additive structure with the highest unsaturation degree known so far along with the in-depth understanding of its breakdown mechanism on those aggressive electrode surfaces. Tripropargyl phosphate (TPP) containing three carbon-carbon triple bonds was found to form dense and protective interphases on both NMC532 cathode as well as graphitic and metallic lithium anodes, leading to significant improvements in performances of both LIBs and lithium metal batteries (LMBs). Comprehensive characterizations together with calculations reveal how the unsaturation functionalities of TPP interact with these electrode chemistries and establish interphases that inhibit gas generation, suppress lithium dendrite growth, and prevent transition metal ion dissolution and deposition on the anode surface. The correlation established among the additive structure, interphasial chemistries, and cell performance will doubtlessly guide us in designing the electrolytes with atomistic precision for future battery chemistries.