Lithium Negative Electrode Research Articles

Numerical Modeling of a Low-Cobalt All-Solid-State Cell with Ceramic Electrolyte Using a Deformable Geometry

All-solid-state batteries with a lithium negative electrode and a ceramic electrolyte are key toward high energy density. To ensure a safe, fast, accurate, and cost-effective development of this technology, the experimental methodology must be supported by the numerical modeling approach. This work proposes and describes an electrochemical model of a Li7La3Zr2O12 (LLZO) and Ni-rich NMC-based lithium cell with a deformable lithium negative electrode. Simulations were computed using the finite element method at different operating conditions to demonstrate the scope of the modeling work. Discharge rate tests, deformation tracking, geometric defect investigation, and polarization decomposition are described. Theoretical validation of the mass balance, the stripping rate, the ohmic polarization, and the mesh deformation demonstrated the consistency of the volumetric deformation strategy. We demonstrated in this study a deformable modeling strategy, which was found to be useful for the electrostripping analysis of anodic geometry defects during discharge. Non-uniformity in the lithium stripping rate was found along the anodic interface with defects, and this non-uniformity was accentuated with a higher discharge rate. The cell’s discharge potential was decomposed by considering the equilibrium potential and the polarizations of the main components of the cell. This post-processing was found to be useful for the understanding of the cell’s behavior.

Strategies for constructing stable solid electrolyte interface on the surface of lithium metal negative electrodes

Abstract With metallic lithium serving as the negative electrode material, lithium metal batteries are seen as the most promising next generation of high-specific energy batteries. However, the poor stability of the solid-state electrolyte interface (SEI) caused by the spontaneous interaction between metal lithium and electrolyte during battery cycling exacerbates several problems such lithium dendrite formation, lower Coulomb efficiency, and capacity degradation. The practical use of secondary lithium metal batteries is therefore constrained. Consequently, enhancing SEI stability is a focus of extensive study in the realm of lithium metal batteries. The ideal surface electrode should have strong surface electrical insulation, good lithium-ion conductivity, and high mechanical strength in order to manage the even deposition of lithium ions on the surface, facilitate ion transport, and inhibit dendritic growth. Therefore, constructing a functional SEI film is an effective strategy to solve the challenges faced by lithium metal negative electrodes. This article first introduces the formation mechanism and structural composition of SEI. Then, the failure reasons of SEI were analyzed. Finally, the modification strategy of SEI was emphasized, aiming to provide a reference for the research of metal lithium negative electrodes.

Electrospun Co-Ni mixed multiple oxidation states heterostructure for high-performance Li-ion battery

With the increasing prevalence of mobile electronic devices, electric vehicles, and other technological advancements, there is a growing demand for higher-capacity Lithium-ion batteries (LIBs). Metal-organic frameworks (MOFs) have been actively researched in recent years due to their numerous advantages. However, the irreversible collapse during lithium-ion interaction hampers MOFs’ electrochemical stability. This study employs a direct precipitation method to synthesize uniformly shaped MOF materials, followed by carbon coating using electrospinning techniques, and ultimately, derivatives of MOF materials are produced through annealing. Thanks to this innovative material design process, exceptional performance is observed in this material as a lithium-negative electrode. After 1000 cycles at a high current density of 1 A g−1, its reversible capacity stabilizes at 1318 mAh g−1. Moreover, this negative electrode material exhibits exceptional rate performance at various current densities. The Co3O4/NiO@NCNFs electrode demonstrates enhanced charge storage capacity due to the synergistic effects of diffusion and capacitance control processes. Additionally, this material exhibits characteristics of low impedance and high lithium-ion diffusion rate. This study presents a novel method for manufacturing lithium-ion battery negative electrode materials by integrating MOF materials with electrospinning technology.

Relating Chemo-Mechanical Hysteresis and Formation Protocols for Anode-Free Lithium Metal Batteries

Cell formation is an energy and time-intensive empirically-guided process crucial to manufacturing secondary lithium-ion batteries. As the rechargeable battery industry moves towards manufacturing lithium metal batteries—where a metallic lithium negative electrode is used instead of a porous graphite composite—the cell formation process may need reconsidering. The effects of formation rate and cycling protocol on lithium metal battery performance are poorly understood. In this work, we used operando acoustic transmission to measure physical changes during the formation cycles and the effect of formation cycling protocols on the long-term cycling of anode-free lithium metal pouch cells—where all the lithium inventory comes from the positive electrode and is deposited as metallic lithium on copper foil during initial charge. We show that a faster C/3 formation protocol results in comparable cycling performance and cell stiffness change to a slower C/10 formation step. Variations in acoustic metrics across different electrolytes tested are attributed to differences in gas formation, cell swelling, and lithium deposition morphology. NMC811 cathodes paired with a high-concentration ether electrolyte are shown to be particularly prone to gas formation, which is mitigated by using a localized high-concentration ether electrolyte and single-crystal NMC532. The results highlight differences in formation behavior between anode-free lithium metal cells and lithium-ion cells. These are important to consider when bringing new manufacturing plants online for lithium metal batteries.

Zinc oxide nanoparticles intercalated with porous carbon as a separator coating for improving the stability of lithium metal anodes.

Metal lithium negative electrodes are considered the "holy grail" of lithium battery negative electrodes due to their ultra-high energy density and low overpotential. However, the arbitrary growth of lithium dendrites during the cycling process hindered its industrialization process. We prepared porous carbon doped with zinc oxide nanoparticles (ZNC-MOF-5) by high-temperature carbonization of MOF-5, and coated ZNC-MOF-5 on the surface of commercial membranes (ZNC-MOF-5@PP). Used to improve the cycling stability of metal lithium negative electrodes. Zinc oxide nanoparticles in ZNC-MOF-5 have good lithium affinity and can promote Li+ deposition. The porous structure with a high specific surface area endows the electrode with high lithium loading capacity, reduces local current density, and obtains a dendrite-free metal lithium negative electrode. The electrochemical cycling performance of Li/Cu batteries indicates that, ZNC-MOF-5@PP. The separator can prevent the growth of dendrites and improve cycling stability, proving that ZNC-MOF-5 can effectively guide the deposition of Li and solve dendrite problems.

Two-birds with one stone: Improving both cathode and anode electrochemical performances via two-dimensional Te-CoTe2/rGO ultrathin nanosheets as sulfur hosts in lithium-sulfur batteries

A Te-doped CoTe2 film could be grown in situ on reduced graphene oxide (rGO) to develop a Te-CoTe2/rGO composite with an ultrathin layered structure, which has multiple protective effects on both the sulfur positive electrode and lithium negative electrode in lithium sulfur (Li-S) batteries. The Te-CoTe2/rGO composite as a sulfur host not only shows a strong adsorbing ability for lithium polysulfides (LiPSs) but can also accelerate the conversion reaction of active material sulfur during the charging/discharging process. More importantly, this host can turn the shuttle effect from an unfavorable factor to a favorable factor, which could improve the electrochemical performance of the lithium anode with uniform lithium plating/stripping resulting from the intermediate polytellurosulfide species (Li2TexSy), which could be generated on the cathode surface via Te reacting with soluble Li2Sn (4 ≤ n ≤ 8). As a result, the S@Te-CoTe2/rGO cathode shows a discharge capacity of 970.0 mA h g−1 in the first cycle at 1 C and retains a high capacity of 545.5 mA h g−1 after 1000 cycles, corresponding to a low capacity decay rate of only 0.043% per cycle. In addition, in situ X-ray diffraction (XRD) and in situ Raman were used to explore the sulfur conversion process. This study not only demonstrates that a two-dimensional (2D) ultrathin Te-CoTe2/rGO composite is successfully developed with multiple effects on Li-S batteries but also opens a new pathway for designing unique sulfur hosts to promote the electrochemical performance of Li-S batteries.

LiAlO2-Modified Li Negative Electrode with Li10GeP2S12 Electrolytes for Stable All-Solid-State Lithium Batteries.

Lithium (Li) metal has an ultrahigh specific capacity in theory with an extremely negative potential (versus hydrogen), receiving extensive attention as a negative electrode material in batteries. However, the formation of Li dendrites and unstable interfaces due to the direct Li metal reaction with solid sulfide-based electrolytes hinders the application of lithium metal in all-solid-state batteries. In this work, we report the successful fabrication of a LiAlO2 interfacial layer on a Li/Li10GeP2S12 interface through magnetic sputtering. As LiAlO2 can be a good Li+ ion conductor but an electronic insulator, the LiAlO2 interface layer can effectively suppress Li dendrite growth and the severe interface reaction between Li and Li10GeP2S12. The Li@LiAlO2 200 nm/Li10GeP2S12/Li@LiAlO2 200 nm symmetric cell can remain stable for 3000 h at 0.1 mA cm-2 under 0.1 mAh cm-2. Moreover, unlike the rapid capacity decay of a cell with a pristine lithium negative electrode, the Li@LiAlO2 200 nm/Li10GeP2S12/LiCoO2@LiNbO3 cell delivers a reversible capacity of 118 mAh g-1 and a high energy efficiency of 96.6% after 50 cycles. Even at 1.0 C, the cell with the Li@LiAlO2 200 nm electrode can retain 95% of its initial capacity after 800 cycles.

Discharge Behavior within Lithium–Sulfur Batteries Using Li–Glyme Solvate Ionic Liquids

Practical use of lithium–sulfur batteries can be realized by using “sparingly solvating electrolytes” such as [Li(G4)][TFSA] (G4, tetraglyme; TFSA, bis(trifluoromethanesulfonyl)amide) solvate ionic liquid, superconcentrated electrolyte solutions, and their hydrofluoroether-diluted electrolytes. On the other hand, the battery performance such as C-rate characteristics of lithium–sulfur batteries is different depending on the electrolyte used. In order to investigate the relationship between the discharge reaction and the battery performance for lithium–sulfur batteries with 1,1,2,2-tertafluoroethyl 2,2,3,3-tetrafluoropropyl ether-diluted [Li(G4)][TFSA], in situ electrochemical impedance spectroscopy has been conducted. During discharge at a high C-rate, a voltage drop was observed in the discharge curve at DOD = 20–35%. The charge transfer resistance of the lithium negative electrode remarkably increased when the voltage drop occurred. Moreover, this increase was only observed for in situ measurements. The charge transfer resistance of the negative electrode is related to the resistance of the Li+ ion dissolution/deposition reaction. During discharging at a high C-rate, the Li+ ion is abundant at the negative electrode interface owing to the changes in the Li+ ion solvation structure, suppressing the Li+ ion dissolution reaction.

Enabling High-Stability of Aqueous-Processed Nickel-Rich Positive Electrodes in Lithium Metal Batteries.

Lithium batteries occupy the large-scale electric mobility market raising concerns about the environmental impact of cell production, especially regarding the use of poly(vinylidene difluoride) (teratogenic) and N-methyl-2-pyrrolidone (NMP, harmful). To avoid their use, an aqueous electrode processing route is utilized in which a water-soluble hybrid acrylic-fluoropolymer together with sodium carboxymethyl cellulose is used as binder, and a thin phosphate coating layer is in situ formed on the surface of the nickel-rich cathode during electrode processing. The resulting electrodes achieve a comparable performance to that of NMP-based electrodes in conventional organic carbonate-based electrolyte (LP30). Subsequently, an ionic liquid electrolyte (ILE) is employed to replace the organic electrolyte, building stable electrode/electrolyte interphases on the surface of the nickel-rich positive electrode (cathode) and metallic lithium negative electrode (anode). In such ILE, the aqueously processed electrodes achieve high cycling stability with a capacity retention of 91% after 1000 cycles (20 °C). In addition, a high capacity of more than 2.5 mAh cm-2 is achieved for high loading electrodes (≈15mg cm-2 ) by using a modified ILE with 5% vinylene carbonate additive. A path to achieve environmentally friendly electrode manufacturing while maintaining their outstanding performance and structural integrity is demonstrated.

Molecular composite electrolytes of polybenzimidazole/polyethylene oxide with enhanced safety and comprehensive performance for all-solid-state lithium ion batteries

Polyethylene oxide (PEO)-based solid polymer electrolyte (SPE) is recognized as the most promising candidate in the commercialization process of all solid lithium ion battery (LIB). However, the crystallization of PEO results in low ionic conductivity, and the poor mechanical property and flammable feature of PEO lead to potential safety hazards in practical use. Here, we propose a cost-efficient, scalable, and facile approach for safe and high-performance SPE based on molecular composite of aromatic polybenzimidazole (PBI) and PEO. The strong intermolecular interactions effectively inhibit the crystallization of PEO, and significantly improve the modulus, strength, and ionic conductivity of PEO electrolyte by 16.6, 11.4, and 3.1 times with the addition 20% PBI. The thermal stability and flame retardancy are also simultaneously improved thanks to the outstanding heat-resistance and noninflammability of PBI. The PBI/PEO electrolyte exhibits excellent interfacial stability to lithium negative electrodes (500 h at 0.3 mA cm−2), and the LiFePO4//Li cell with PBI/PEO electrolyte shows a high-rate performance (152 mAh g−1 at 0.2 C) as well as cycling performance (100 cycles at 0.2 C) at 60 °C. We believe that the PBI/PEO molecular composite electrolytes hold great promising for practical application in safe and high-performance all-solid-state LIB.

The polymer composite electrolyte with polyethylene oxide-grafted graphene oxide as fillers toward stable highcurrent density lithium metal anodes

Adding inorganic fillers to polymer electrolytes is one of the main means to improve ionic conductivity. However, the filler will aggregate, causing the problem of incompatibility between the electrolyte and the metal lithium negative electrode. According to reports, the flaky structure of graphene oxide (GO) has the characteristics of large specific surface area and stable performance, which has attracted widespread attention as a filler for polymer electrolytes. However, the electrolyte membrane has poor compatibility with lithium negative electrodes when GO as a filler, which is not conducive to the full performance of lithium batteries. In this paper, we grafted polyethylene oxide (PEO) on the surface of GO (the product is referred to as GO@PEO) to improving the dispersibility of the filler and the compatibility of the gel polymer electrolyte (GPE) with lithium metal . It is worth that after GO grafting PEO, the impedance of the interface between GPE and lithium metal is significantly reduced, and the compatibility of the electrolyte with the lithium negative electrode is significantly improved. Assembled into Li/ Li battery, the surface current cycle is stable, up to 1 mA cm−2. GO@PEO further improves the ionic conductivity of the ion conductivity up to 1.6 mS cm−1. Further prepared into LiFePO4 (LFP)/Li battery, GPE-GO@PEO showed excellent cycle stability and the discharge specific capacity retention rate was 95.6% after 100 cycles. The rate performance of the battery is also significantly improved. At 5C, the discharge specific capacity of the LFP/Li battery remains 40 mAh g−1.

In-situ detection of LiMn2O4 dissolution during electrochemical cycling by

Herein we describe a modified Swagelok electrochemical cell for characterizing individual electrode behavior as part of full cell operation, including individual electrode potentials and dissolution phenomena. The case study presented is that of the non-aqueous Li-LiMn2O4 system. Outcomes from the work include characterization of lithium negative electrode potential variation with applied current, lithium corrosion and passivation in the electrolyte, and LiMn2O4 dissolution with cycling. It is also demonstrated that Mn(III) is the dissolution product. Application of the technique to other systems, including electrode materials and electrolytes, is discussed.

Insight into the Solid Electrolyte Interphase Formation in Bis(fluorosulfonyl)Imide Based Ionic Liquid Electrolytes

AbstractThe formation of the solid electrolyte interphase (SEI) in an ionic liquid electrolyte of 0.5 m lithium bis(fluorosulfonyl)imide (LiFSI) in 1‐ethyl‐3‐methylimidazolium bis(fluorosulfonyl)imide at high cell voltages (1.7–1.9 V) is investigated in ordered mesoporous carbon (OMC) based Li metal cells using an operando small‐angle neutron scattering (SANS) technique coupled with electrochemical impedance spectroscopy and ex situ X‐ray photoelectron spectroscopy (XPS). It is demonstrated that discharging the OMC Li metal cells to ≈2 V and holding the cell voltage constant induces a rapid current increase with time, confirming extensive reduction and SEI formation. XPS analysis reveals that LiF is formed at open cell voltage (OCV), which is attributed to the carbenes generated at the lithium negative electrode because of its reaction with EMIm cation diffusing to and initiating the reaction with FSI− anions at the carbon positive electrode. It is confirmed that the chemical reaction at OCV and electrochemical reduction at high cell voltage of the FSI− anion plays a protective role against EMIm cation co‐intercalation into the carbon positive electrode during the initial discharge. Operando SANS studies also suggest that slight differences occur in the surface composition and reaction mechanism as a function of cell voltage.

Comparison of Lithium Salt Effect on Negative Electrodes and Lithium–Air Cell Performance

The cycle stability of lithium negative electrodes for Li–air secondary batteries was studied under oxygen atmosphere using Li∣Li symmetric cells with three organic electrolyte solutions: 1.0 M LiCF3SO3/tetraglyme (G4), 1.0 M LiN(SO2CF3)2/G4, and 1.0 M LiNO3/G4. Of these, 1.0 M LiNO3/G4 showed excellent stability without dendrite deposition, even for increased dissolution/deposition capacity from 0.50 to 2.0 mAh cm−2. These results are considered to be due to the stable Li2O passivation layer that was formed, not only by the direct reaction with oxygen, but also by the action of NO3 − as an oxidant, which released NO2 − as a redox mediator. Li–O2 cells with 1.0 M LiNO3/G4 showed a clear charging voltage plateau at 3.7 V, which evidenced the redox mediator effect of NO2 −, and cell cycleability was enhanced to 25 cycles.

Synergy between LiNO3 and Tetraglyme-Sulfone Dual-Solvent Electrolyte Solutions in Li-O2 Batteries

LiNO3 has been widely studied as a redox mediator to reduce positive electrode overvoltage during charging of lithium/air (O2) batteries. LiNO3 has a bifunctional effect as a redox mediator for the positive electrode and as a surface modifier for the lithium negative electrode. The dissociation of LiNO3 electrolyte salt was enhanced by using a mixed solvent of tetraglyme and a sulfone with a high dielectric constant. This extended the charging voltage plateau because the mixed solvent enhanced the oxidation of into NO2 in the 1.0 M LiNO3 electrolyte solution. The viscosities of the sulfone-containing electrolyte solutions decreased and their ionic conductivities increased as the temperature increased. Therefore, Walden plots for the electrolyte solutions containing sulfones were parallel to the ideal line, meaning that the dissociation of LiNO3 was unaffected by temperature due to the strong solvation of ethyl methyl sulfone and tetramethylene sulfone to Li+ ions. Consequently, the sulfone-containing electrolyte solutions delivered better charging performance than an electrolyte solution of simple tetraglyme at 50 °C.

The application of Cr-MOF@MWCNT modified separator in high-performance lithium-sulfur batteries

Lithium-sulfur batteries have attracted attention when competing with the next-generation of rechargeable batteries due to their higher theoretical specific capacity, lower cost, and non-toxic and harmless feature. However, there are many obstacles towards the practical application of lithium-sulfur batteries such as low conductivity of the positive electrode and discharge products, the “shuttle effect” of polysulfides, and the unsafety of the lithium negative electrode. In this paper, Cr-MOF@MWCNT as a separator modification layer is introduced into lithium-sulfur batteries to solve the problem of “shuttle effect”. The Cr-MOF in the coating layer can adsorb polysulfides, and the MWCNT tightly combined with Cr-MOF helps to build a good conductive network, so that the adsorbed polysulfides can be converted. As the initial specific capacity and cycle stability of lithium-sulfur batteries with the Cr-MOF@MWCNT separators have been improved, the initial specific capacity is as high as 1377 mAh g−1 at a rate of 0.2 C, while the average capacity attenuation per cycle after 300 cycles is 0.14%, with 99.8% of coulombic efficiency.

Redox Mediator Effects of LiNO3 in Tetraglyme-Sulfone Dual Solvent Electrolyte Solution on Li-O2 Battery Performance

Lithium-oxygen (LOB) batteries still have many issues, although they possess a large theoretical energy density of 3500 Wh kg-1. Among the issues, we focused on the large overvoltage on charging to cause serious energy loss and short cycle life. Recently, redox mediator (RM) has been attracting much attention and studied intensively. The RM can chemically oxidize discharge product, Li2O2, at a lower potential compared to that without RM. LiNO3 is a unique RM among various kinds of RM, because it works not only as a RM for the positive electrode (PE), but also as a surface modifier for the lithium negative electrode (NE).In our recent paper we demonstrated that dimethylsulfoxide (DMSO) revealed a preferable effect to reduce overvoltage as the second solvent of tetraglyme (G4)-based LiNO3 electrolyte solution [1]. This result is attributed to the strong solvation of DMSO due to its high dielectric constant, while the complicated behavior of NO3⁻/NO2⁻ and other nitrogen oxide chmical species can be elucidaed on the basis of a reaction scheme summaried as follows [2].2Li + NO3⁻ → NO2⁻ + Li2O (1)NO2⁻ →NO2 + e⁻ (2)NO2 + Li2O2 → NO2⁻ + Li+ + LiO2 (3)Therefore, we further studied on the effect of the second solvent for G4-based LiNO3 eletrolyte solution by comparing some of sulfone solvents with DMSO for the purpose to understand the working mechanism of LiNO3 as the RM and to enhance the LOB performance.Four kinds of solvents were used in this study: G4 (dielectric constant ε=7.7), DMSO (ε=48), ethyl methyl sulfone (EMS, ε=55), and tetramethylene sulfone (TMS, ε=43). G4 was mixed with one of other solvents in the volume ratio of 7:3 or 5:5 for 1 M LiNO3/G4-based electrolyte.Swagelok cells were used for LOB cell test, consisting of a PE with Ketjen Black (KB) and PVDF binder coated on a carbon paper, a Li foil NE, Celgard 2400 separator intervening the two electrodes, and the electreolyte solution prepared as dscribed above. Simple galvanostatic mode was applied to the cell tests between 2.0 and 4.5 V.All of the LOB cells with the dual solvent electrolyte solution showed suppressed charging voltage plateaus at around 3.5 V, suggesting the reacion of equation (2) followed by equation (3) to oxidize Li2O2. These results evidenced the critical effect of dissociation of LiNO3 and diffusivity of NO2⁻ ions in the electrolyte solutions on the performance of the LOB. Moreover, the cell temperature elevation up to 50℃ amplified the effect and its difference among DMSO, EMS and TES, which comfirmed us the importance of the diffusivity of NO2⁻ and the suppression of NO2 consuming side reactions. We will discuss on the whole picture of the working mechanism of the LiNO3 RM referring other data such as physicochemical properties of the electrolyte, diffuivity of Li+ by NMR, analysis of the electrodes by SEM-EDS and XRD. This study was supported by JST “Next Generation Batteries Area in Advanced Low Carbon Technology Research and Development Program (ALCA)” from MEXT, Japan Reference s : [1] Y. Hayashi, M. Sohmiya, Y. Kubo, and M. Saito, et al., J. Electrochem. Soc.,167, 020542 (2020).[2] V. S. Bryantsev, J. Uddin, G. V. Chase, and Dan Addison, et al., J. Am. Chem. Soc., 136, 3087 (2014).

Electrochemical impedance spectroscopy study of lithium–sulfur batteries: Useful technique to reveal the Li/S electrochemical mechanism

Electrochemical impedance spectroscopy (EIS) study was done in order to go deeper into the electrochemical processes of Li/S battery in a common CR2032 coin-type cell. In order to separate the contributions of each electrode (i. e. lithium negative electrode and sulfur composite positive electrode), impedance measurements on symmetrical cells consisting of two previously cycled electrodes was used. This methodology enables to propose an overall interpretation of the different electrochemical phenomena present during cycling. Low temperature tests were also applied, which brought fruitful information concerning the kinetics of the reactions and allowed to confirm the chemical-physical interpretations performed on the cell cycled at 25°C.

Hydroxyapatite nanowires composite interlayer based on aramid fiber paper for Li-S batteries

Lithium-sulfur (Li-S) batteries have higher discharge specific capacity and low cost, which is considered to be the most promising lithium-ion battery in the next generation, but the current shuttle effect is still the biggest obstacle to commercial production. In this work, hydroxyapatite (Ca5(PO4)3(OH)) nanowires were prepared by hydrothermal synthesis and formed a hierarchical cross-linked network structure with aramid fiber paper (AP) to hinder the diffusion and dissolution of polysulfides, thereby effectively improving the electrochemical performance of the battery. HN adsorbs polysulfides by using chemical bonds such as hydroxyl groups and inhibits their diffusion to lithium negative electrodes; AP with 3D porous structure not only allows HN to adhere well to the surface, but also captures soluble polysulfides. The electrochemical test results showed that the primary discharge capacity of electrode with HNAP interlayer reached 1456 mAh/g at a rate of 0.05C. The remarkable cycling stability was obtained, the high reversible capacity of 840 mAh/g with negligible fading rate of 0.0243% per cycle at 1C were obtained after 200 cycles.

(Invited) Advanced Hybrid Supercapacitors with “Water-in-Salt” Electrolyte and Protected Lithium Anode

Aqueous supercapacitors are attracting increasing attention owing to their high power density, cyclability and environmental friendliness. However, thermodynamic limit of water electrolysis limits the cell voltage and window of common aqueous supercapacitors, restricting the energy density. We have previously demonstrated that advanced hybrid supercapacitors that employ aqueous electrolyte with a multi-layered water-stable protected negative electrode consisting of laminated metallic lithium or lithiated graphite, polymer electrolyte and water-stable lithium ion conducting solid electrolyte Li1+x+yTi2-xAlxSiyP3-yO12 (LTAP), can extend the negative electrode potential close to 0 V vs Li/Li+, thus providing a cell voltage close to 4 V with aqueous catholytes. In this work this hybrid supercapacitor concept is further extended to high concentration electrolytes or “water-in-salt (WIS)” electrolytes. We will demonstrate that 4 V-class cell voltage with wide voltage window can be delivered for advanced hybrid supercapacitors with capacitive or pesudocapacitive positive electrodes in WIS electrolytes combined with a protected Li anode. A typical advanced hybrid supercapacitor with MnO2 electrode shows a 4.4 V maximum cell voltage with a 1.5 V window, an energy density of 405 Wh/(kg-MnO2) at a power density of 0.88 kW kg/(kg-MnO2). A high energy density of 163 Wh kg/(kg-MnO2) is maintained at a power density of 16.7 kW kg/(kg-MnO2). These advanced hybrid supercapacitors show acceptable cycle stability and good energy retentions (around 90% within 3000 cycles). Fig. Galvanostatic charge/discharge curves for advanced hybrid supercapacitor with MnO2 in 21m LiTFSI and protected lithium negative electrode at (a) a current density of 0.1 mA/cm2 and U cell varized from 1.0 to 1.5 V (U min = 2.9 V and U max = 3.9→4.4 V) and (b) a fixed U cell = U max – U min = 4.4 – 2.9 V = 1.5 V) and various current densities (Left axis: cell voltage; Right axis: electrode potentials of MnO2 electrode and multi-layered water-stable protected lithium anode). (c) Specific capacity (1) and capacitance (2) extracted from the discharge curves of MnO2 electrode from advanced hybrid supercapacitor with MnO2 in 1 M Li2SO4 at U cell = U max – U min = 4.3 – 3.3 V = 1.0 V. Specific capacity (3) and capacitance (4) extracted from the discharge curves of MnO2 electrode from advanced hybrid supercapacitor with MnO2 in 21 m LiTFSI at the U cell = U max – U min = 4.4 – 2.9 V = 1.5 V. Figure 1