Conventional Carbonate-based Electrolytes Research Articles

Tailoring Solvation Solvent in Localized High-Concentration Electrolytes for Lithium||Sulfurized Polyacrylonitrile.

Sulfurized polyacrylonitrile (SPAN) is a promising cathode material for lithium-sulfur (Li-S) batteries due to its significantly reduced polysulfide (PS) dissolution compared to that of elemental S cathodes. Although conventional carbonate-based electrolytes are stable with SPAN electrodes, they are unstable with Li metal anodes. Recently, localized high-concentration electrolytes (LHCEs) have been developed to improve the stability of Li anodes. Here, we report a new strategy to further improve the performance of Li||SPAN batteries by replacing the conventional solvating solvent 1,2-dimethoxyethane (DME) in LHCEs with a new solvating solvent, 1,2-diethoxyethane (DEE). The new optimal DEE-LHCE exhibits less reactivity against Li2S2, alleviates PS dissolution, forms a better cathode-electrolyte interphase layer on the SPAN cathode, and enhances SPAN structural reversibility even at elevated temperatures (45 °C). Compared to DME-LHCE, DEE-LHCE with the same salt and diluent leads to better performance in Li||SPAN batteries (with 82.9% capacity retention after 300 cycles at 45 °C), preservation of the SPAN cathode structure, and suppression of volume change of the Li metal anode. A similar strategy on tailoring the solvating solvents in LHCEs can also be used in other rechargeable batteries to improve their electrochemical performances.

Revealing the key role of non-solvating diluents for fast-charging and low temperature Li-ion batteries

Fast-charging and low temperature operation are of vital importance for the further development of lithium-ion batteries (LIBs), which is hindered by the utilization of conventional carbonate-based electrolytes due to their slow kinetics, narrow operating temperature and voltage range. Herein, an acetonitrile (AN)-based localized high-concentration electrolyte (LHCE) is proposed to retain liquid state and high ionic conductivity at ultra-low temperatures while possessing high oxidation stability. We originally reveal the excellent thermal shielding effect of non-solvating diluent to prevent the aggregation of Li+ solvates as temperature drops, maintaining the merits of fast Li+ transport and facile desolvation as at room temperature, which bestows the graphite electrode with remarkable low temperature performance (264 mA h g−1 at −20 °C). Remarkably, an extremely high capacity retention of 97% is achieved for high-voltage high-energy graphite||NCM batteries after 250 cycles at −20 °C, and a high capacity of 110 mA h g−1 (71% of its room-temperature capacity) is retained at −30 °C. The study unveils the key role of the non-solvating diluents and provides instructive guidance in designing electrolytes towards fast-charging and low temperature LIBs.

A dicarbonate solvent electrolyte for high performance 5 V-Class Lithium-based batteries

Rechargeable lithium batteries using 5 V positive electrode materials can deliver considerably higher energy density as compared to state-of-the-art lithium-ion batteries. However, their development remains plagued by the lack of electrolytes with concurrent anodic stability and Li metal compatibility. Here we report a new electrolyte based on dimethyl 2,5-dioxahexanedioate solvent for 5 V-class batteries. Benefiting from the particular chemical structure, weak interaction with lithium cation and resultant peculiar solvation structure, the resulting electrolyte not only enables stable, dendrite-free lithium plating-stripping, but also displays anodic stability up to 5.2 V (vs. Li/Li+), in additive or co-solvent-free formulation, and at low salt concentration of 1 M. Consequently, the Li | |LiNi0.5Mn1.5O4 cells using the 1 M LiPF6 in 2,5-dioxahexanedioate based electrolyte retain >97% of the initial capacity after 250 cycles, outperforming the conventional carbonate-based electrolyte formulations, making this, and potentially other dicarbonate solvents promising for future Lithium-based battery practical explorations.

Realizing High-Performances Sb Anodes for K-Ion Batteries

Alloy anodes have long been considered promising alternatives to carbon counterparts for high-energy K-ion batteries (KIBs) as they could uptake several ions per K atom through alloying reactions, delivering exceptional capacities at low voltage. However, alloy electrodes usually undergo severe volume expansion upon large K ion insertion, which will trigger the pulverization of active particles and the breakage of solid electrolyte interphase (SEI), leading to rapid capacity degradation. Instead of fabricating nanostructured materials, novel electrolyte formulations can be used to realize stable cycling of high-capacity anodes in KIBs. Sb is a promising low-cost anode material for KIBs, possessing a high theoretical capacity of 660 mAh g-1 at average voltage of about 0.5V toward K+/K. However, it shows rapid capacity degradation in conventional carbonate-based electrolytes. To stabilize the Sb anodes, novel ether-based KIB electrolytes are designed to replace the conventional ones, enabling a high reversible capacity over 180 cycles. It is found that a thinner and amorphous SEI, with abundant oligomer-like species, is built in ether base electrolytes. Such SEI is more elastic, and can effectively wrap the Sb particles to accommodate repeated volumetric changes, and preventing copious electrolytes decomposition. These findings allow us to develop crucial fundamental knowledge to design ideal SEIs for stabilizing alloy anodes to boost the energy densities of today’s alkali-metal ion batteries.

Locally Concentrated Ionic Liquid Electrolytes for Lithium/Sulfurized Polyacrylonitrile Batteries

Low-cost sulfurized polyacrylontrile (SPAN), which shows negligible polysulfide dissolution and stable cycling up to hundreds of cycles due to a solid-phase mechanism in carbonate-based electrolytes, is a valuable high-energy cathode material for long-lifespan lithium metal batteries (LMBs).1 -3 However, the conventional carbonate-based electrolytes for commercial lithium-ion batteries are incompatible with lithium metal anodes (LMAs).4 The unstable solid-electrolyte interphases (SEIs) result in lithium dendrite growth and low lithium stripping/plating CEs, which further cause safety concerns and limited lifespan of Li/SPAN cells with low negative to positive areal capacity (N/P) ratio. Therefore, the development of Li/sulfurized polyacrylonitrile (SPAN) batteries requires electrolytes that can form stable electrolyte/electrode interphases (EEIs) simultaneously on lithium metal anodes (LMAs) and SPAN cathodes. With the remarkable compatibility toward LMAs and low flammability,4–7 locally concentrated ionic liquid electrolytes (LCILEs) might be promising candidates for Li/SPAN cells.Herein, a low-flammability locally concentrated ionic liquid electrolyte (LCILE) employing monofluorobenzene (mFBn) as the diluent is proposed for Li/SPAN cells.8 Unlike non-solvating diluents in other LCILEs, mFBn partially solvates Li+, decreasing the coordination between Li+ and bis(fluorosulfonyl)imide (FSI-). In turn, this triggers a more substantial decomposition of FSI- and consequently results in the formation of a SEI rich in inorganic compounds, which enables a remarkable Coulombic efficiency (99.72%) of LMAs. Meanwhile, a protective cathode/electrolyte interphase (CEI), derived mainly from FSI- and organic cations, is generated on the SPAN cathodes, preventing the dissolution of polysulfides. Benefiting from the robust interphases simultaneously formed on both the electrodes, highly stable cycling of Li/SPAN cells for 250 cycles with a capacity retention of 71% is achieved employing the LCILE and only 80% lithium metal excess.

Borate-Based Artificial Solid-Electrolyte Interphase Enabling Stable Lithium Metal Anodes.

Lithium (Li) metal is considered as the "holy grail" of anode materials for next-generation high energy batteries. However, notorious dendrite growth and interfacial instability could induce irreversible capacity loss and safety issues, limiting the practical application of Li metal anodes. Herein, we develop a novel approach to construct a borate-based artificial solid-electrolyte interphase (designated as B-SEI) through the reaction of metallic Li with triethylamine borane (TEAB). According to our cryogenic electron microscopy (Cryo-EM) characterization results, the artificial SEI adopts a glass-crystal bilayer structure, which facilitates uniform Li-ion transport and inhibits dendrite growth during Li plating. Benefiting from such an artificial SEI, the Li anode delivers an improved rate performance and prolonged cycle life. The symmetric Li/B-SEI||Li/B-SEI cell can maintain stable cycling for 700 h at a high current density of 3 mA cm-2. The full-cell pairing Li/B-SEI with LiFePO4 only exhibits minimal capacity decay after 500 cycles in a conventional carbonate-based electrolyte. This work demonstrates the feasibility of building a boride-based artificial SEI to stabilize the Li metal anode based on microscopic characterization results and comprehensive electrochemical data, which represents a promising avenue to develop practical Li metal batteries.

Co-Intercalation Batteries (CoIBs): The Use of TiS2 As Electrode for Solvent Co-Intercalation in Sodium-Ion Batteries

With the rising demand for lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) have become an attractive alternative with the promise of improved safety, reduced cost, and lower environmental impact.1 However, the larger ion size of sodium cation has major consequence on the battery chemistry, which provides several challenges and opportunities for designing electrode materials and electrolyte solutions.2 Graphite is the currently most used anode material in LIBs. However, its use in SIBs, with traditional carbonate-based electrolytes, results in very poor specific capacities due to unfavorable thermodynamic processes.3 A strategy around this problem is to choose different solvents: Ethers and in particular glymes can exhibit a co-intercalation behavior into the graphite structure by forming ternary graphite intercalation compounds.4, 5 Although the co-intercalation of solvent molecules with sodium cation leads to a large increase in the graphite framework, the cycle life and rate capability of the reaction are excellent.Regardless of this, there is a lack of evidence for a comparable reaction with other electrode materials. Hence, it would be of interest to identify a cathode material that operates via this same mechanism. A battery based on solvent co-intercalation at both electrodes can have minimized charge-transfer resistances due to the absence of desolvation steps, and great cycle life. Thus, such a system can show high power density over many cycles. It has also been shown that stripping of the solvation shell can be the rate limiting step for battery operation, especially at subzero temperatures.6 Such a solvent co-intercalation battery (CoIB) could therefore be more energy efficient compared to other batteries or could enable a better low-temperature performance.Transition metal dichalcogenides (TMDs) have emerged as promising anode materials owing to their low cost, high electric conductivity, good thermal stability and environmental friendliness. Among them, titanium sulphide (TiS2), with a two-dimensional framework, exhibits several advantages such as a high conductivity (compare to other metal oxides), a larger interlayer distance (0.569 nm) compared to graphite (0.335 nm) and high stability. 7 Several papers have reported on the use of TiS2 as an anode material for SIBs, and observed that the voltage profiles and electrochemical behaviour of the system is highly dependent on the choice of electrolyte. However, this has seldomly been explicitly stated and the cause of the electrolyte dependence has never been investigated. By using operando and in-situ techniques such as Operando XRD and dilatometry, Na-diglyme complexes were showed to co-intercalate, similar as graphite, into TiS2. In contrast, no signs of solvent co-intercalation are observed in cyclic ethers and conventional carbonate-based electrolytes – where instead the redox reaction with TiS2 results in the formation of different NaxTiS2 compounds.As we identified TiS2 as “co-intercalation electrode” in glyme-based electrolytes it served to create the first ever solvent co-intercalation battery (CoIB – pronounced Co-IB) which was done by pairing TiS2 (positive electrode) with graphite (negative electrode).8 This work could enable the development of highly energy efficient batteries with minimum charge transfer resistances and References I. Hasa, S. Mariyappan, D. Saurel, P. Adelhelm, A. Y. Koposov, C. Masquelier, L. Croguennec and M. Casas-Cabanas, J. Power Sources, 2021, 482, 228872. P. Adelhelm, P. Hartmann, C. L. Bender, M. Busche, C. Eufinger and J. Janek, Beilstein Journal of Nanotechnology, 2015, 6, 1016-1055. B. Jache and P. Adelhelm, Angew. Chem., 2014, 126, 10333-10337. B. Jache, J. O. Binder, T. Abe and P. Adelhelm, Physical Chemistry Chemical Physics, 2016, 18, 14299-14316. M. Goktas, C. Bolli, J. Buchheim, E. J. Berg, P. Novák, F. Bonilla, T. f. Rojo, S. Komaba, K. Kubota and P. Adelhelm, ACS applied materials & interfaces, 2019, 11, 32844-32855. S. S. Zhang, K. Xu and T. R. Jow, Journal of Power Sources, 2003, 115, 137-140. Q. Yun, L. Li, Z. Hu, Q. Lu, B. Chen and H. Zhang, Adv. Mater., 2020, 32, 1903826. G. A. Ferrero, G. Avall, K. A. Mazzio, Y. Son, K. Janssen, S. Risse and P. Adelhelm, Adv. Energy Mater., 2022, 2202377. an improved low temperature performance, where the charge transfer can become rate limiting. Figure 1

Eutectic Electrolytes Composed of Li Salt and Sulfones

Sulfone-based highly concentrated electrolytes are promising electrolytes for high-voltage Li-ion batteries (LIBs), owing to the high thermal and oxidative stabilities of sulfones. In addition, highly concentrated Li salt/sulfone electrolytes exhibit unique Li+ ion hopping/exchange conduction mechanism and high Li+ ion transference number (>0.6).1,2 However, the application of these electrolytes at low temperatures is limited due to the precipitation of a stable crystalline solvate. In this study, the applicability of ternary mixtures of Li salt, sulfolane (SL), and dimethyl sulfone (DMS) as LIB electrolytes was assessed. Due to the increased entropy of mixing, the crystallization of the solvates was suppressed in the ternary electrolytes, resulting in a wide temperature range of liquid sate of the electrolytes.3 In the ternary electrolytes, the network structures of Li+–sulfone–Li+ and Li+–anion–Li+ were formed, and Li+ ion dynamically exchanges sulfones and anions and diffuses more rapidly than these ligands, resulting in a relatively high Li+ transference number. Highly reversible charge–discharge behaviors of the LiCoO2 and graphite electrodes were attained using the ternary electrolyte. Despite the lower ionic conductivity of the sulfone-based electrolyte, the rate capability of the Li/LiCoO2 cell with the ternary electrolyte was comparable to that in a conventional carbonate-based electrolytes. Acknowledgements This study was partially supported by the JSPS KAKENHI (Grant No. JP19H05813 and JP22H00340). References K. Dokko et. al., J. Phys. Chem. B 2018, 122, 10736.Y. Ugata et. al., J. Phys. Chem. B 2021, 125, 6600.Y. Ugata et. al., J. Phys. Chem. C 2022, 126, 10024.

Tunning solvation structure in non-flammable, localized high-concentration electrolytes with enhanced stability towards all aluminum substrate-based K batteries

Although metallic potassium or graphite anode with low redox potentials are desirable for potassium-ion batteries (PIBs), the severe capacity decay caused by consecutive reduction reactions on the aggressively reactive anode surface is inevitable because of the scarcity of an effective passivation layer. Additionally, the development of PIBs faces potential safety hazards due to the usage of reactive anodes with flammable electrolytes. Herein, a fire-retardant localized high-concentration electrolyte (LHCE) is formulated by adding a low-polarity co-solvent of highly fluorinated ether into the concentrated potassium bis(fluorosulfonyl)imide/trimethyl phosphate. A unique electrolyte solvation environment with the enhanced anion-cation interaction in an LHCE facilitates a durable anion-derived solid electrolyte interphase (SEI) with self-accelerated interfacial kinetics and minimizes the SEI dissolution compared to the conventional carbonate-based electrolyte. Consequently, the unmodified Al substrate could sustain stable potassium metal cycling above 3400 h (over 800 cycles) with high reversibility (98%), and the graphite anode retains prolonged cyclic stability (over 300 cycles) with a high reversible capacity (257.6 mAh g−1) and capacity retention (92.6 % at 0.2 C). Meanwhile, Al corrosion at high voltage is significantly suppressed, and the electrochemical window is extended due to less free solvents in an LHCE, enabling good electrolyte compatibility with high-voltage cathodes. Coupling non-flammable solvents and the concept of LHCE could facilitate a better understanding of electrolyte chemistry and offer more opportunities to use K or graphite anode for all Al substrate-based PIBs highlighted with high performance and superb safety.

Sodium hydride inspired the clarification of the ether-carbonate solvent disparity in sodium metal anodes

Ether-based electrolytes enable highly reversible sodium (Na) plating/stripping behavior while conventional carbonate-based electrolytes deliver rather poor electrochemical compatibility with Na metal anodes. Yet, this ether-carbonate mystery in Na metal anodes is still not fully elucidated. Sodium hydride (NaH) has been recently demonstrated to be a key chemical component on the cycled Na metal anodes. In this work, via the combination of time of flight-second ion mass spectroscopy (ToF-SIMS) and on-line D2O titration mass spectroscopy, we disclose the spatial distribution of NaH and quantify its amount in Na metal anodes cycled in ether-based and carbonate-based electrolytes. A systematic study reveals that NaH accumulates upon continuous Na plating-stripping in conventional carbonate electrolytes, and the NaH formation is proved to be highly correlated with the evolution of H2 during cell operation. The huge performance disparity of Na metal anodes in ether-based and carbonate-based electrolytes is ascribed to the fact that much less NaH and H2 is produced in the case of ether-based electrolytes. This work enriches the understanding of interfacial chemistries of Na metal anodes and highlights the importance of minimizing the generation of NaH and H2 in protecting Na metal anodes.

Stabilizing Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode by generating ion-conductive polymer coating layer with 1, 3-dioxolane introducing electrolyte for lithium-ion batteries

The employment of electrolyte-film forming additive is a facile and effective strategy to improve the cycling performance of aggressive Nickel-rich layered oxide cathode LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode for high energy lithium-ion batteries (LIBs). Here we report a homogeneous and dense polymer cathode-electrolyte-interface (CEI) film generated via in-situ electrooxidation polymerization of 1, 3-Dioxolane (DOL) in a conventional carbonate-based electrolyte. It is found that the electrolyte modification with 15% DOL is the most effective in balancing the interfacial stability and Li-ion diffusion kinetics of NCM811 cathode, while also achieving its comparable rate capability and greatly improving cycling performance. Morphological and elemental characterizations demonstrate that the 15% DOL-derived CEI layer not only alleviates the impacts of harmful interfacial reactions and hinders the particle disintegration, but also suppresses the irreversible lattice transition of the NCM811 cathode surface to the inactive rock salt phase. Moreover, it is proved that the F-rich interfacial layer displays excellent Li-ion transport kinetics. As a result, the cell exhibits high capacity retention of 85.2% and 78.1% after 200 cycles at cut-off voltages of 4.3 V and 4.5 V at 1 C in the 15% DOL-modified electrolyte. Therefore, creating a stable and effective Li-ion conductive interfacial protective film on the cathode surface by optimizing an electrolyte functional additive is an economical and available approach to develop the highly stabilized Ni-rich cathode for high-energy LIBs applications.

Lithium Manganese Sulfates as a New Class of Supercapattery Materials at Elevated Temperatures.

To make supercapattery devices feasible, there is an urgent need to find electrode materials that exhibit a hybrid mechanism of energy storage. Herein, we provide a first report on the capability of lithium manganese sulfates to be used as supercapattery materials at elevated temperatures. Two compositions are studied: monoclinic Li2Mn(SO4)2 and orthorhombic Li2Mn2(SO4)3, which are prepared by a freeze-drying method followed by heat treatment at 500 °C. The electrochemical performance of sulfate electrodes is evaluated in lithium-ion cells using two types of electrolytes: conventional carbonate-based electrolytes and ionic liquid IL ones. The electrochemical measurements are carried out in the temperature range of 20-60 °C. The stability of sulfate electrodes after cycling is monitored by in-situ Raman spectroscopy and ex-situ XRD and TEM analysis. It is found that sulfate salts store Li+ by a hybrid mechanism that depends on the kind of electrolyte used and the recording temperature. Li2Mn(SO4)2 outperforms Li2Mn2(SO4)3 and displays excellent electrochemical properties at elevated temperatures: at 60 °C, the energy density reaches 280 Wh/kg at a power density of 11,000 W/kg. During cell cycling, there is a transformation of the Li-rich salt, Li2Mn(SO4)2, into a defective Li-poor one, Li2Mn2(SO4)3, which appears to be responsible for the improved storage properties. The data reveals that Li2Mn(SO4)2 is a prospective candidate for supercapacitor electrode materials at elevated temperatures.

Surface modification using heptafluorobutyric acid to produce highly stable Li metal anodes

The Li metal is an ideal anode material owing to its high theoretical specific capacity and low electrode potential. However, its high reactivity and dendritic growth in carbonate-based electrolytes limit its application. To address these issues, we propose a novel surface modification technique using heptafluorobutyric acid. In-situ spontaneous reaction between Li and the organic acid generates a lithiophilic interface of lithium heptafluorobutyrate for dendrite-free uniform Li deposition, which significantly improves the cycle stability (Li/Li symmetric cells >1200 h at 1.0 mA cm−2) and Coulombic efficiency (>99.3%) in conventional carbonate-based electrolytes. This lithiophilic interface also enables full batteries to achieve 83.2% capacity retention over 300 cycles under realistic testing condition. Lithium heptafluorobutyrate interface acts as an electrical bridge for uniform lithium-ion flux between Li anode and plating Li, which minimizes the occurrence of tortuous lithium dendrites and lowers interface impedance.

Highly Soluble Lithium Nitrate-Containing Additive for Carbonate-Based Electrolyte in Lithium Metal Batteries

While lithium nitrate (LiNO3) is widely utilized as an electrolyte additive in ether-based electrolytes for stable lithium deposition, use of LiNO3 in conventional carbonate-based electrolytes is very limited due to the poor solubility of LiNO3 in the carbonate-based electrolytes. Herein, a new LiNO3-containing electrolyte additive which is very soluble in carbonate-based electrolytes, 1-trimethylsilyl imidazole lithium nitrate adduct (TMSILN), has been synthesized by a simple method. The electrochemical performance is significantly improved in Li/Li and NCM622/Li cells with TMSILN additive containing electrolyte. Our extensive investigations reveal that the deposited lithium metal in the TMSILN additive-containing electrolyte has a circular morphology with a very thin (∼5 nm) surface film containing lithium nitrate decomposition products such as Li3N and LiNxOy. The improved electrochemical performance can be ascribed to the favorable features of the SEI and morphology of the deposited lithium in the presence of the TMSILN additive.

Flavone as a novel multifunctional electrolyte additive to improve the cycle performance of high-voltage LiNi0.5Mn1.5O4 batteries

The high operating voltage of LiNi0.5Mn1.5O4 (LNMO) material poses a challenge to conventional carbonate-based electrolyte, whose continuous decomposition leads to the fast capacity fading of battery. Herein, flavone (FLA) as a novel multifunctional electrolyte additive is introduced into basic electrolyte (1.0 M LiPF6 - ethylene carbonate + dimethyl carbonate) to significantly improve the cycle performance of LNMO/Li battery. Experiments and density functional theory (DFT) calculations manifest that FLA can be preferentially oxidized and reduced to generate stable surface films to ameliorate the decomposition of other electrolyte solvent. Besides, the FLA-derived Li2CO3-rich surface films can improve interfacial stability and ensure high ionic conductivity. In addition, FLA is more inclined to react with HF compared with EC and DMC, thereby alleviating LNMO corrosion and transition metal ions dissolution by HF, and consequently enhance the stability of bulk structure. The preferential reduction of FLA contributes to the formation of a stable passivation layer with high ionic conductivity on Li anode, which is conducive to uniform lithium deposition during the cycling and prolonging battery cycle life. The cycle performances of LNMO/Li and LNMO/Graphite batteries using the electrolyte containing 1 wt% FLA are significantly improved compared with those using basic electrolyte.

Multifunctional surface-engineering of 3D-lithiophilic nanocarbon scaffold for high-voltage anode-minimized lithium metal batteries

A lithium metal anode (LMA) offers the lowest negative potential and a high specific/volumetric capacity; however, it promotes the decomposition of electrolyte and leads to poor Coulombic efficiency, particularly in a conventional carbonate-based electrolyte which is electrochemically stable at high voltage; >4 V (vs Li+/Li). Herein, we report the development of a catalytic support to realize a high-performance LMA, suitable for use in carbonate-based electrolyte systems, consisting of a 3D carbon nanofiber scaffold (3D-CNS) coated with LiNO3. The lithium-rich inorganic coating preferentially decomposes on the surface of the 3D-CNS during initial lithiation, forming an inorganic compound–rich, solid–electrolyte interface (SEI) layer before any electrolyte decomposes. The LiNO3-derived SEI layer not only inhibits side reactions that consume electrolyte but also improves lithium-ion transport kinetics, leading to LMAs with high CE and superior rate capability. In addition, residual LiNO3 promotes the uniform deposition/dissolution of lithium during cycling, facilitating stable cycling over 300 cycles. Moreover, a lithium metal battery featuring a high-voltage NCM811 cathode and a LMA based on the proposed support with minimal excess lithium loading demonstrates significantly improved cycling performance with high energy and power densities of ∼ 570 Wh kg−1 and ∼ 690 W kg−1, respectively.

Innovative discontinuous-SEI constructed in ether-based electrolyte to maximize the capacity of hard carbon anode

Compared with graphite, the lower sodiation potential and larger discharge capacity of hard carbon (HC) makes it the most promising anode material for sodium-ion battery. Utilizing ether-based electrolyte rather than conventional carbonate-based electrolyte, HC achieves superior electrochemical performance. Nevertheless, the mechanism by which ether-based electrolyte improves the properties of HC is still controversial, primarily focusing on whether it forms solid electrolyte interphase (SEI) film. In this work, according to the sodium storage mechanisms in HC at low voltage (<0.1 V), including Na+-diglyme co-interaction into the carbon layer (SEI forbidden) and desolvated Na+ insertion in the irregular carbon holes (SEI required), the NaPF6 concentration in ether-based electrolyte was regulated, so as to construct a discontinuous-SEI on the surface of the HC anode, which significantly enhances the electrochemical performances of HC. Specifically, with 0.2 M NaPF6 ether-based electrolyte, HC deliverers a discharge capacity of 459.7 mA h g−1 at 0.1 C and stays at 357.2 mA h g−1 after 500 cycles at 1 C, which is substantially higher than that of higher/lower salt concentration electrolytes.

Nonflammable all-fluorinated electrolytes enabling high-power and long-life LiNi0.5Mn1.5O4/Li4Ti5O12 lithium-ion batteries

LiNi0.5Mn1.5O4 (LNMO)/Li4Ti5O12 (LTO) spinel-spinel batteries have appealing features of high energy, high power and inherent safety. However, cycling high-voltage LNMO cathodes causes severe oxidation of conventional carbonate-based electrolytes and leads to extensive capacity decay. Herein, we report that a nonflammable all-fluorinated electrolyte can support high-rate and inherent-safe 3.2 V LNMO/LTO batteries. The nanoscale fluorinated interphase stabilizes cathodic structure and suppresses side reactions during cycling, even at a high cutoff voltage of 5.0 V. The LNMO/Li cell in the all-fluorinated electrolyte delivers superior cyclability with 90.8 % capacity retention at 1 C over 1000 cycles. The LNMO/LTO cell exhibits great practical potential with capacity retention greater than 93.0 % over 1500 cycles at 5 C. In addition, the all-fluorinated electrolyte allows the LNMO/LTO cells to operate over wide temperatures. This work highlights a facile method for realizing the commercialization of LNMO/LTO lithium-ion batteries.

Constructing solid electrode-electrolyte interfaces in high-voltage Li|LiCoO2 batteries under dual-additive electrolyte synergistic effect

High-voltage lithium metal batteries (LMBs) using lithium cobalt oxide (LCO) as cathode can deliver the coveted high energy density, but come at a sacrifice of cycling stability due to the unstable electrode/electrolyte interphase and LCO instability at high voltage. Here, we demonstrate a modified conventional carbonate-based electrolyte for Li|LCO LMBs by simply introducing vinylene carbonate (VC) and KBF4 as the organic/inorganic dual-additive. In a synergistic way, the dual-additive is capable of helping to generate thin and dense cathode electrolyte interphase (CEI) on LCO, effectively alleviating the drastic electrolyte decompositions at high voltage, as well as the irreversible transition from O3 to H1-3 phase, Co dissolving, and structure collapse of LCO. Meanwhile, the corrosion layer on Li anode is also mitigated due to the dual-additive-derived solid electrolyte interphase (SEI) film. Based on the dual-additive electrolyte, the assembled 4.6 V Li|LCO LMB achieves promising long-term cycling performance with a capacity retention of 91.1% after 300 cycles at 1 C (1 C = 274 mA g−1). The simple and effective electrolyte engineering strategy can promote the development of high-voltage lithium metal batteries.

1-D Modeling of an Electroactive Electrolyte for Advanced Primary and Secondary Li Batteries

In the search for more energy- and power- dense battery materials, the cathode is most often the component that is engineered to boost operating voltage and capacity. However, new approaches to battery design have yielded performance improvements by designing electrolytes with reactive species that increase capacity and energy density of full-cells. These approaches borrow insights from commercial battery technologies such as Pb-H2SO4, Li-SO2, or Li-SOCl2, where the cathodic reaction involves liquid-phase active species1–3, while employing solid-phase cathode materials.To better understand how specific examples of electroactive electrolytes improve rather than impede performance, our work focuses on two battery chemistries: a primary Li-CFx cell with an irreversible electrolyte reaction, and a secondary Li-LMR cell with a reversible electrolyte reaction. For each case, we develop a 1-D COMSOL model to investigate how the reaction of electrolyte species affects cell impedance, impacts Li cation transport, alters the electrolyte conductivity, and finally how each of these mechanistically impact the energy and power density of the cell. Our modeling work is complemented by experimental studies that measure important electrolyte and cathode properties at various states of discharge or cycling.(1) Park, H.; Lim, H.-D.; Lim, H.-K.; Seong, W. M.; Moon, S.; Ko, Y.; Lee, B.; Bae, Y.; Kim, H.; Kang, K. High-Efficiency and High-Power Rechargeable Lithium–Sulfur Dioxide Batteries Exploiting Conventional Carbonate-Based Electrolytes. Nat. Commun. 2017, 8 (1), 14989. https://doi.org/10.1038/ncomms14989.(2) Schlaikjer, C. R.; Goebel, F.; Marincic, N. Discharge Reaction Mechanisms in Li / SOCl2 Cells. J. Electrochem. Soc. 1979, 126 (4), 513–522. https://doi.org/10.1149/1.2129078.(3) Ruetschi, P. Aging Mechanisms and Service Life of Lead–Acid Batteries. J. Power Sources 2004, 127 (1–2), 33–44. https://doi.org/10.1016/j.jpowsour.2003.09.052.