Cathode Mixture Research Articles

Effect of Cu As an Additive in the MnO2 Cathode in Rechargeable Zn-MnO2 Alkaline Batteries

Introduction Aqueous rechargeable Zn-MnO2 batteries are drawing much attention as a solution for grid-scale energy storage because of their characteristics of high safety, low cost, and ease of manufacturing [1]. However, in alkaline aqueous solutions, due to the formation of electrochemically inactive compounds such as hausmannite (Mn3O4) during the charging/discharging process [2], developing highly rechargeable Zn-MnO2 alkaline batteries remains a challenge.In 2017, Yadav et al. reported that they successfully achieved the full theoretical 2-electron capacity of MnO2 for >6000 cycles by adding bismuth oxide (Bi2O3) and copper to the MnO2 cathode to form Bi-intercalated (Bi-δ-MnO2) intercalated with Cu2+ ions [3]. Some researchers are paying attention to the effect of Bi2O3 as an additive. However, the study on the role of Cu is still incomplete. Objective To unravel the effect of Cu as an additive, we used MnO2, MnO2 + Cu, and MnO2 + Bi2O3 + Cu as active materials to observe the electrochemical behaviors in the alkaline electrolyte without the existence of [Zn(OH)4]2−. Moreover, we investigated the product of each cycled cathode.In this study, we have mainly focused on the effects of adding Cu to the MnO2 cathode without Bi2O3. Experimental The cathode mixture is made by mixing the active materials, acetylene black (AB) and polytetrafluoroethylene (PTFE) by hands at the weight ratio of 80:14:6. Electrolytic manganese dioxide (EMD), EMD + the powder of metallic Cu (6:2 wt%), and EMD + Bi2O3 + Cu (6:1:2 wt%) were mixed and used as the active materials. A 2-electrolyte Zn-MnO2 cell was used for electrochemical measurements. The cathode mixture, Zn plate, and Hg/HgO electrode were used as the working electrode, the counter electrode, and the reference electrode, respectively. Solutions of 6 mol dm−3 (M) KOH and 6 M KOH saturated with ZnO are used as the cathode electrolyte and the anode electrolyte, respectively. FAAM-PK-75 was used as the separator between the two electrolytes. The galvanostatic test was performed at 0.2C (1C = 616 mA g−1) for 20 cycles in a voltage range of −1.0 – 0.45 V (vs. Hg/HgO). Results and discussion The galvanostatic data of the EMD + Cu and EMD cathodes is shown in Fig. 1. The plateau at around −250 mV, which indicates the oxidation of MnⅡ during the charging process, was observed at the fifth cycle. In contrast, such plateau cannot be observed in the case of the EMD cathode. However, the capacity retention at the seventh cycle for the EMD + Cu cathode is lower than that for the EMD cathode (Fig. 2). We suggest that Cu not only induces the second electron reaction of Mn but also the formation of electrochemically inactive compounds. Furthermore, other Cu compounds are expected to be formed rather than metallic Cu because of the poor reversibility of the EMD + Cu cathode after discharge. From the XPS result for the EMD + Cu discharged cathode, the Cu2+ satellite peak was hardly observed, which shows no existence of the possibly formed compound CuMn2O4. Based on the results, we conclude that the electrochemically inactive compounds formed in the cycled EMD + Cu cathode are Mn3O4 and Cu2O instead of any Cu-Mn compounds. Since Cu induces the second electron reaction of Mn, the species of MnⅡ, such as Mn(OH)2 and [Mn(OH)4]2− increase, which finally allows MnⅢ species to encounter MnⅡ species easier and form Mn3O4. Conclusion We found that the MnO2 + Cu cathode shows poorer cyclability even compared to the MnO2 cathode. We assume that this is because while Cu induces the second electron reaction of MnO2, it does not prevent the formation of Mn3O4, which deteriorates the performance of the Zn-MnO2 cells. Moreover, no Cu-Mn compounds were found in the XPS result.

Selective Metal Recovery: Innovating Leaching from Lfp-NMC Cathode Mixtures in Lithium-Ion Batteries

Lithium-ion batteries lie at the heart of the energy transition and electric mobility. In the coming years, numerous gigafactories and recycling plants will be constructed worldwide to produce and recycle batteries for electric vehicles. While recycling plants currently focus on batteries for electric vehicle, there will also be a need to develop the recycling industry for smaller batteries, such as those used in electric bicycles, a market that is rapidly expanding. The chemical processes required to recycle these batteries may not necessarily be the same as those for batteries in electric vehicle due to differences in the composition of the materials to be processed. For electric vehicles, the composition will be well established as the materials will mainly come from either NMC (LiNixMnyCozO2) or LFP (LiFePO4) technologies. However, for batteries in electric bicycle and electric scooter, the materials to be processed will be a mix of NMC and LFP technologies. Therefore, it will be necessary to develop a flexible process capable of extracting metals from the feed which the composition will vary. Furthermore, the hydrometallurgical processes used to treat these materials must be capable of recovering cobalt, nickel, manganese, and lithium despite the presence of varying and significant concentrations of iron, which is generally challenging in hydrometallurgy.This talk will demonstrate how we can take advantage of the physicochemistry of transition metals in the presence of phosphate to develop an effective leaching process that selectively dissolves cobalt, nickel, manganese, and lithium from mixtures of NMC and LFP, resulting in a sufficiently pure leachate to facilitate downstream purification steps through liquid-liquid extraction after leaching.

Correlative Survey of Blended LiCoO2 and LiMn2O4 Cathode Materials for Lithium-ion Batteries

We employed the lithium-ion battery model in Multiphysics to simulate the electrochemical characteristics of lithium-ion batteries. These batteries consist of a cathode mixture comprising LiCoO2 and LiMn2O4, as well as quasi-graphite anode. Our simulations successfully replicated the discharge profiles of both unblended and blended cathodes across different current rates, aligning with results obtained from experiments. The energy and power densities of the blended cathode framework were regulated by adjusting the mix ratio in the simulation model. Additionally, the blended electrodes of LiCoO2 and LiMn2O4 demonstrated an above-average electrochemical performance, combining the characteristics of the two active materials.Keywords: Lithium-ion Battery; Blended Cathode Active Materials; Simulation; Experiment

Linking Microstructure and Ionic/Electronic Conductivity in Composite Cathodes for Thiophosphate-Based All-Solid-State Lithium-Ion Batteries

Compared to conventional lithium-ion batteries (LIBs) with liquid electrolytes, ASSBs (all-solid-state batteries) have the potential to improve safety and achieve higher performance and energy density1. However, there are still many challenges to tackle in order to achieve ASSBs with sufficient cell performance, and one of them is to optimize the microstructure regarding its ionic and electronic conductivity. To achieve a high energy density, the fraction of AM must be as high as possible, and pores must be avoided. At the same time, an ionic conductive network of the SE has to be established; thus, both phases have to be distributed homogeneously with the composite cathode. On the other hand, the degradation of the solid electrolyte (SE) with cathode active material (CAM) and conductive additive (CA) has to be tackled with protective coatings that hinder the degradation but at the same time, keep the charge transport pathways open2,3. Therefore, the composite cathode microstructure (i.e., composition ratios CAM:SE:CA, particle characteristics, distribution of the phases) must be designed for different materials systems to ensure the sufficient percolation of ions and electrons for high performance4-9.In this study, we aim to understand the effect of the CAM fraction, morphology, and coating on the transport properties within the composite cathode. For this purpose, effective ionic and electronic conductivity of different cathode mixtures of Li6PS5Cl and NMC622 (coated, uncoated, single crystal, polycrystal) were analyzed and correlated with the microstructures. Moreover, a conductive matrix comprising Li6PS5Cl and C65 was introduced to the composite cathode system. Electronic and ionic conductivities were measured via impedance spectroscopy with ion- or electron-blocking electrodes in a symmetric cell configuration under constant pressure. To do so, a specially designed cell setup comprising a force sensor and a spring to adjust the pressure was used. The impedance spectra were fitted using T-type transmission line model (TLM) with equivalent circuit components with the RelaxIS 3 software package. Microstructural characterization was conducted on the powder mixtures and Ar- polished cross sections via scanning electron microscope using a transfer shuttle. We found the ionic and electronic transport limitations for the prepared composite cathode mixtures by varying the abovementioned parameters and optimized the CAM fraction accordingly. The results presented contribute to an improved understanding of the structure-property relationships and provide guidance on how to design a suitable microstructure.for improved cell performance. Acknowledgement The authors gratefully acknowledge the support of the German Federal Ministry of Education and Research within the program “FH‐Impuls” (Project SmartPro, Subproject SMART‐BAT, Grant no. 13FH4I07IA), Dr. Veit Steinbauer (Aalen University), Sebastian Puls and Dr. Nella Vargas-Barbosa (Helmholtz Institute Münster (IEK-12) - Forschungszentrum Jülich). References Janek, Jürgen, and Wolfgang G. Zeier.,Nature Energy 1.9 (2016): 1-4.Ma, Yuan et al., Advanced Functional Materials 32.23 (2022): 2111829.Sun, Shuo et al., Materials Futures 1.1 (2022): 012101.Noh, Sungwoo et al., Journal of Electroceramics 40 (2018): 293-299.Dewald, Georg F., et al., Batteries & Supercaps 4.1 (2021): 183-194.Ohno, Saneyuki, and Wolfgang G. Zeier., Accounts of Materials Research 2.10 (2021): 869-880.Bielefeld, Anja, Dominik A. Weber, and Jürgen Janek., ACS applied materials & interfaces 12.11 (2020): 12821-12833.Dixit, Marm et al., Solid State Batteries Volume 2: Materials and Advanced Devices. American Chemical Society, 2022. 113-132.Hendriks, Theodoor A. et al. ," Batteries & Supercaps (2023): e202200544

Electrochemical Stability of Li5.4(PS4)(S0.4Cl1.0Br0.6) in an All-Solid-State Battery Comprising LiNbO3-Coated Li(Ni0.8Co0.1Mn0.1)O2 Cathode and Lithium Metal Anode

All-solid-state lithium-ion batteries are a promising next-generation technology because they have higher energy densities than their liquid-electrolyte counterparts. Recently, halogen-rich argyrodite, specifically Li5.4(PS4)(S0.4Cl1.0Br0.6), has been reported to show higher ionic conductivities than other sulfides with argyrodite structures and electrochemical stability against lithium metal. However, the stability of Li5.4(PS4)(S0.4Cl1.0Br0.6) against cathode active materials in all-solid-state batteries has not yet been evaluated. Herein, we report the electrochemical stability of Li5.4(PS4)(S0.4Cl1.0Br0.6) as a solid electrolyte in an all-solid-state battery. Li(Ni0.8Co0.1Mn0.1)O2 and lithium metal were used as the cathode and anode, respectively, and an enhancement in the discharge capacity was expected. The impedance of the battery was almost independent of the frequency above 106 Hz for 50 charge/discharge cycles. These findings are a result of the constant lithium-ion resistance of Li5.4(PS4)(S0.4Cl1.0Br0.6). X-ray diffraction analysis confirmed that no byproduct phase was formed in the cathode mixture over 50 cycles. These results demonstrate the high chemical stability of Li5.4(PS4)(S0.4Cl1.0Br0.6) against Li(Ni0.8Co0.1Mn0.1)O2, thereby broadening the design scope of electrolyte materials for all-solid-state lithium-ion batteries with high performance and stability.

ELECTROREDUCTION OF NICKEL(II) CHLORIDE, COBALT(II) FLUORIDE AND MOLYBDENUM(VI) OXIDE MIXTURES IN A HEAT ACTIVATED BATTERY

The discharge characteristics of the elements of a thermally activated chemical current source (HAB) containing NiCl2–CoF2–MoO3 mixtures as a positive electrode are investigated. It is established that molybdenum oxide stabilizes the discharge plateau and increases the discharge voltage at temperatures above 530°C. The discharge curve has a stepwise character. The number of steps of the discharge curve is determined by the operating conditions of HAB. The low-voltage stage (less than 0.4 V) corresponds to the reduction of lithium molybdates, which are formed by the interaction of molybdenum oxide with the reduction products of transition metal halides. A study of the cathode reduction products by the methods of XRD, STA and SEM was carried out. It is established that during the discharge of the HAB element, the initial components of the cathode mixture are restored to metals that form a dendritic matrix. The DSC curves of the salt fraction formed during electrochemical reactions have a number of thermal effects corresponding to the temperatures of joint melting of a triple mixture of lithium halides LiF–LiCl–LiBr and eutectic dual systems LiF–LiCl, LiCl–Li2O, in which transition metal halides and lithium molybdates are dissolved.

Mechanistic Studies on CO2 Electroreduction on Ni{M}x-YSZ and Ce{M}Ox-YSZ

The conversion of CO2 to fuels via electroreduction can be instrumental in reducing dependence on fossil fuels and contributes to the global targets of CO2 reduction. The electrochemical reduction of CO2 to hydrocarbons, however, is kinetically limited by the fact that it is a multi-step process, with each step requiring the transfer of multiple electrons. On the other hand, the high temperature electrochemical reduction of CO2 to CO using a solid oxide electrolysis cell (SOEC) provides a route that is both energy efficient and cost effective. The CO thus produced can act as a value added product, as it can be directly used as a fuel, or it can be reduced into hydrocarbons via the well-known Fischer-Tropsch process. Ni/YSZ based electrodes are fairly ubiquitous in the field of solid oxide technologies. We have proposed the infiltration of Cu into Ni/YSZ to generate Ni{Cu}x-YSZ type cathodes, which exhibit improved performance for CO2 electroreduction at high temperature (~800 oC). The electrodes are prepared on commercial standard YSZ supports using Ni{Cu}x-YSZ mixtures for cathode and LSM-YSZ mixture for anode.Most of the existing studies on high temperature reduction of CO2 on Ni/YSZ have been in the presence of safe gases, such as H2 or CO. The presence of H2 in the inlet stream created a reducing atmosphere on the electrode surface, and the reduction of CO2 proceeded through a thermochemical reverse water gas shift (RWGS) mechanism. (CO2 + H2 à CO + H2O). The presence of CO could lead to catalyst deactivation by Carbon deposition through Boudouard reaction (2CO à CO2 + C). Observations from such experiments led to the belief that metallic Ni in Ni/YSZ acts as the active species for CO2 reduction; and that the oxidation of the Ni to NiO leads to deactivation of the catalyst. By using operando Raman spectroscopy and online mass spectrometry, we have countered this idea and demonstrated that the electroreduction of CO2 on Ni-YSZ is mediated by a layer of NiOx on the electrode surface, which is the actual active species. CeOx is a well-known cathodic material for pure CO2 electroreduction. We have attempted to study the mechanistic aspects associated with CO2 electroreduction on Ce{M}Ox based systems as well. Figure 1

Dry Battery Electrode Manufacturing Enabled By Continuous Powder Mixing

Lithium-Ion Battery electrode manufacturing is a cost- and energy-intensive process that usually relies on the use of a hazardous and expensive solvent, N-methyl-2-pyrrolidone (NMP), for cathodes. After coating the battery-slurry to a current collector, the solvent needs to be evaporated to obtain a porous electrode suitable for the use in a Lithium-Ion Battery. The solvent is a processing material and unwanted in the final product. In fact, solvent residues can fuel parasitic side-reactions within the battery cell and hence deteriorate battery lifetime and safety. The utilization of NMP in battery production plants demands costly labor protection and explosion safety measurements during mixing and coating and necessitates a highly energy and floor-space demanding drying step using thermic drying ovens of up to 100 meters.[1] For ecological and economic reasons, NMP is not emitted in large-scale production facilities, but condensed and recycled by distillation. The NMP-recovery system adds additional floor space and energy demand to the production site. The drying and solvent recovery can account for up to 39% of the total energy demand of a Lithium-Ion Battery Cell production and therefore produce significant CO2 emissions.[2] A solvent-free, dry electrode manufacturing that eliminates the use of solvents hence reduces the floor space, energy demand and cost of a production plant and eases safety and environmental concerns. Different approaches have been reported in the literature to put dry coating into practice,[3],[4] yet most strategies, for example spray coating or brush coating, lack of a feasible implementation into large scale production. In contrast, a dry coating approach that is sometimes referred to as the Maxwell-Process is, according to media reports, currently installed at Tesla’s Gigafactories in Berlin and Austin.[5] In fact, a publicly available teardown of a Tesla 4680 battery cell hints that a dry coated anode could already be used in commercial vehicles.[6] Compared to the state-of-the-art electrode manufacturing process, dry coating requires different polymeric binder systems that form spiderweb-like structures of fine fibrils connecting the electrochemical active particles and the conductive additive particles. PTFE is highly suitable since it is stable towards typical electrolytes and cathode materials and is known to easily form fibrils. These properties are also utilized to produce expanded PTFE membranes like Gore-Tex. The fibril-network in the battery context is primarily formed by a high-shear dry mixing process. The powder mixture is then compressed to a free-standing electrode film (powder-to-film) by a heated rolling mill (calender) and the resulting film is ultimately laminated to a current collector foil (film-to-foil). We demonstrate that a twin screw-extruder can be used to tune the degree of binder-fibrillation during dry-mixing of NMC-based cathode mixtures. Extrusion based mixing allows to use powder mixtures with little amounts of PTFE binder (1 wt%) to produce self-supporting, free-standing cathode films and, ultimately, battery electrodes with high flexibility and sufficient mechanical stability. We show a superior rate-performance and cycling-stability of single-layer pouch cells with dry-coated cathodes compared to cells with wet coated reference electrodes of likewise composition and electrode design. Possible causes for the improved performance focusing on microstructural electrode properties are discussed.[1] Westphal, Bastian G.; Kwade, Arno (2018): Critical electrode properties and drying conditions causing component segregation in graphitic anodes for lithium-ion batteries. In: Journal of Energy Storage 18, S. 509–517.[2] Erik Emilsson, Lisbeth Dahllöf (2019): Lithium-Ion Vehicle Battery Production. IVL Swedish Environmental Research Institute.[3] Duffner, Fabian; Kronemeyer, Niklas; Tübke, Jens; Leker, Jens; Winter, Martin; Schmuch, Richard (2021): Post-lithium-ion battery cell production and its compatibility with lithium-ion cell production infrastructure. In: Nat Energy 6 (2), S. 123–134.[4] Verdier, Nina; Foran, Gabrielle; Lepage, David; Prébé, Arnaud; Aymé-Perrot, David; Dollé, Mickaël (2021): Challenges in Solvent-Free Methods for Manufacturing Electrodes and Electrolytes for Lithium-Based Batteries. In: Polymers 13 (3).[5] https://www.tagesspiegel.de/berlin/tesla-coup-mit-giga-berlin-neue-technologie-soll-wasserverbrauch-minimieren/27244032.html[6] https://www.youtube.com/watch?v=8WPPBhqeekw Figure 1

Front Cover: Tailoring Electrolyte Distributions to Enable High‐performance Li3PS4‐based All‐solid‐state Batteries under Different Operating Temperatures (Chem. Asian J. 12/2023)

Li3PS4 shows great potential as a solid electrolyte for all-solid-state lithium batteries due to its high Li-ion conductivity and excellent mechanical properties. All-solid-state lithium batteries using the synthesized Li3PS4 electrolytes combined with Li3InCl6 electrolytes with good electrochemical/chemical stability, which acts both as the Li-ion additive in the cathode mixture and as an isolation layer to isolate the direct contact between the sulfide electrolytes and bare LiNi0.6Mn0.2Co0.2O2 active materials, deliver a superior electrochemical performance. More information can be found in the Research Article by Chuang Yu, Long Zhang et al.

Tailoring electrolyte distributions to enable high-performance Li3PS4-based all-solid-state batteries under different operating temperatures.

Li3PS4 shows great potential as solid electrolyte for all-solid-state lithium batteries (ASSLBs) due to its high conductivity and excellent mechanical properties. However, its poor interfacial stability with bare high-nickel materials in the cathode mixture inhibits the energy density and electrochemical performances of the correspondingLiNi0.6Mn0.2Co0.2O2/Li3PS4/Li-In battery. The Li3InCl6 electrolyte with good electrochemical/chemical stability with bare NCM622, which acts both as a Li-ion additive in the cathode and as an isolation layer to isolate the direct contact between the sulfide electrolytes and active materials, providing superior solid/solid interface stabilities in the assembled battery. XPS and TEM results confirm that this strategy can mitigate the side reactions.This grading utilization of different solid electrolytes can greatly alleviate the poor electrochemical stability, yielding smaller interfacial resistances. The corresponding battery delivers high discharge capacities at various C-rates under different operating temperatures. It delivers a much higher initial discharge capacity of 187.7 mAh g-1at 0.1C with a coulombic efficiency of 87.6% at RT. Moreover, it can show highly reversible capacity with excellent cyclability when operated at 0 and -20 oC. This work provides a hierarchical utilization strategy to fabricate sulfide electrolytes-based ASSLBs with high energy density and superior cycling performance combined with highly-oxidation cathode materials.

Microscopic Degradation Mechanism of Argyrodite-Type Sulfide at the Solid Electrolyte-Cathode Interface.

Interfacial engineering of sulfide-based solid electrolyte/lithium-transition-metal oxide active materials in all-solid-state battery cathodes is vital for cell performance parameters, such as high-rate charge/discharge, long lifetime, and wide temperature range. A typical interfacial engineering method is the surface coating of the cathode active material with a buffer layer, such as LiNbO3. However, cell performance reportedly degrades under harsh environments even with a LiNbO3 coating, such as high temperatures and high cathode potentials. Therefore, we investigated the interfacial degradation mechanism focusing on the solid electrolyte side for half cells employing the cathode mixture of argyrodite-type Li6PS5Cl/LiNbO3-coated LiNi0.5Co0.2Mn0.3O2 exposed at 60 °C and 4.25 and 4.55 V vs Li/Li+ using transmission electron microscopy/electron diffraction (TEM/ED) and X-ray absorption spectroscopy (XAS). The TEM/ED results indicated that the ED pattern of the argyrodite structure disappeared and changed to an amorphous phase as the cells degraded. Moreover, the crystal phases of LiCl and Li2S appeared simultaneously. Finally, XAS analysis confirmed the decrease in the PS4 units of the argyrodite structure and the increase in local P-S-P domains with delithiation from the interfacial solid electrolyte, corresponding to the TEM/ED results. In addition, the formation of P-O bonds was confirmed during degradation at higher cathode potentials, such as 4.55 V vs Li/Li+. These results indicate that the degradation of this interfacial region determines the cell performance.

Slurry-Coated LiNi0.8Co0.1Mn0.1O2-Li3InCl6 Composite Cathode with Enhanced Interfacial Stability for Sulfide-Based All-Solid-State Batteries.

The implementation of all-solid-state lithium batteries (ASSLBs) is regarded as an important step toward the next-generation energy storage systems. The sulfide solid-state electrolyte (SSE) is a promising candidate for ASSLBs due to its high ionic conductivity and easy processability. However, the interface stability of sulfide SSEs toward high-capacity cathodes like nickel-rich layered cathodes is limited by the interfacial side reaction and narrow electrochemical window of the electrolyte. Herein, we propose introducing the halide SSE Li3InCl6 (LIC) with high (electro)chemical stability and superior Li+ conductivity to act as an ionic conductive additive in the Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM) cathode mixture through a slurry coating, aiming to build a stable cathode-electrolyte interface. This work demonstrates that the sulfide SSE Li5.5PS4.5Cl1.5 (LPSCl) is chemically incompatible with the NCM cathode, and the indispensable role of the substitution of LPSCl with LIC in enhancing the interfacial compatibility and oxidation stability of the electrolyte is highlighted. Accordingly, this new configuration shows superior electrochemical performance at room temperature. It shows a high initial discharge capacity (136.3 mA h g-1 at 0.1C), cycling performance (77.4% capacity retention at the 100th cycle), and rate capability (79.3 mA h g-1 at 0.5C). This work paves the way for investigating interfacial challenges regarding high-voltage cathodes and provides new insights into possible interface engineering strategies.

Achieving high-performance Li6.5Sb0.5Ge0.5S5I-based all-solid-state lithium batteries

Sb-based lithium sulfide electrolytes are promising for all-solid-state lithium battery applications due to their ultrahigh Li-ion conductivity (10−2 S/cm) which is even comparable to current liquid electrolytes. However, the poor electrochemical stability between this electrolyte and high voltage layered structure cathode makes it difficult to achieve excellent battery performances. Herein, Li6.5Sb0.5Ge0.5S5I electrolyte with ionic conductivity up to 10 m S/cm is successfully synthesized and the electrochemical failure mechanism of the corresponding battery using bare LiNi0.6Mn0.2Co0.2O2 cathode and Li-In anode is revealed. Furthermore, Li3InCl6 electrolyte is introduced both as an ionic additive in the cathode mixture and as an isolating layer to avoid side reactions. The designed configuration delivers a high discharge capacity of 162.7 mAh/g at 0.5C and sustains 74.5% of the capacity after 200 cycles at room temperature. Moreover, it also can reversibly cycle from -20 to 60 °C with superior battery performances. This work provides a general design strategy for utilizing highly conductive sulfide electrolytes with low stability in all-solid-state batteries.

Degradation Analysis by X-ray Absorption Spectroscopy for LiNbO3 Coating of Sulfide-Based All-Solid-State Battery Cathode.

The surface coating of cathode active material in all-solid-state batteries using sulfide-based solid electrolytes is well-known to be a fundamental technology, and LiNbO3 is one of the most representative materials. The half cells using the cathode mixture of Li6PS5Cl/LiNbO3-coated LiNi0.5Co0.2Mn0.3O2 were exposed in harsh conditions at 60 °C and 4.25-4.55 V vs Li/Li+ and analyzed by transmission electron microscope/energy dispersive X-ray spectroscopy (TEM/EDS) and X-ray absorption spectroscopy (XAS). TEM/EDS observation shows that Nb element derived from LiNbO3 coating had remained at the interface, which means that Nb element had not migrated to the solid electrolyte and active material. On the other hand, the XAS spectra of Nb L3-edge changed corresponding to cell performance degradation. From the comparison with the spectra of the reference materials of the Li-Nb-O system, the XAS spectral changes were assigned to the decomposition reaction which released Li and O from the LiNbO3 coating. The side reaction is presumed to cause to the oxidization deterioration of sulfide electrolyte at the interface of Li6PS5Cl/LiNbO3-coated LiNi0.5Co0.2Mn0.3O2.

Unraveling Electrochemical Stability and Reversible Redox of Y-Doped Li 2 ZrCl 6 Solid Electrolytes

Lithium halide electrolytes show great potential in constructing high-energy-density solid-state batteries with high-voltage cathode materials due to their high electrochemical stability and wide voltage windows. However, the high cost and low conductivity of some compositions inhibit their applications. Moreover, the effect of electronic additives in the cathode mixture on the stability and capacity is unclear. Here, the Y 3+ doping strategy is applied to enhance the conductivity of low-cost Li 2 ZrCl 6 electrolytes. By tailoring the Y 3+ dopant in the structure, the optimal Li 2.5 Zr 0.5 Y 0.5 Cl 6 with high conductivity up to 1.19 × 10 −3 S cm −1 is obtained. Li 2.5 Zr 0.5 Y 0.5 Cl 6 @CNT/Li 2.5 Zr 0.5 Y 0.5 Cl 6 /Li 5.5 PS 4.5 Cl 1.5 /In-Li solid-state batteries with different carbon nanotube (CNT) contents in the cathode are fabricated. The stability and electrochemical performances of the cathode mixture as a function of CNT content are studied. The cathode mixture containing 2% (wt.) CNT exhibits the highest stability and almost no discharge capacity, while the cathode mixture consisting of Li 2.5 Zr 0.5 Y 0.5 Cl 6 and 10% (wt.) CNT delivers a high initial discharge capacity of 199.0 mAh g −1 and reversible capacities in the following 100 cycles. Multiple characterizations are combined to unravel the working mechanism and confirm that the electrochemical reaction involves the 2-step reaction of Y 3+ /Y 0 , Zr 4+ /Zr 0 , and Cl − /Cl x − in the Li 2.5 Zr 0.5 Y 0.5 Cl 6 electrolyte. This work provides insight into designing a lithium halide electrolyte-based cathode mixture with a high ionic/electronic conductive framework and good interfacial stability for solid-state batteries.

Enabling superior electrochemical performances of Li10SnP2S12-based all-solid-state batteries using lithium halide electrolytes

Li10GeP2S12 shows great potential as solid electrolytes for solid-state batteries due to its ultrahigh Li-ion conductivity. However, the high cost of Ge and the poor stability limit its applications. Replacing Ge with Sn can significantly lower the cost and maintains the high conductivity, while the corresponding Li10SnP2S12 still suffers the low interfacial stability with the bare high voltage layered oxide cathodes. Herein, Li10SnP2S12 with high Li-ion conductivity up to 4.79 mS cm−1 has been synthesized. All-solid-state battery using the cathode consisting of bare LiNi0.6Co0.2Mn0.2O2 and Li10SnP2S12 shows low capacities and poor cyclability due to side reactions between those two particles. To improve the interfacial stability, a highly conductive Li3InCl6 electrolyte is introduced both in the cathode mixture and between the cathode layer and Li10SnP2S12 solid electrolyte layer. This new configuration delivers superior electrochemical performances at different operating temperatures. It delivers high initial discharge capacities of 176.1 mAh g−1, 186.9 mAh g−1, and 73.7 mAh g−1 at 0.1C when operated at room temperature, 60 oC, and −20 oC, respectively. The superior battery performances are attributed to the excellent electrochemical stability of Li3InCl6 electrolyte towards bare LiNi0.6Co0.2Mn0.2O2 cathode. This work provides a guideline to design Li10SnP2S12-based all-solid-state lithium batteries with high energy density and long span life.

Unraveling the LiNbO3 coating layer on battery performances of lithium argyrodite-based all-solid-state batteries under different cut-off voltages

The coating layer can effectively mitigate the undesirable side effects that occur at the active material/sulfide electrolyte interface in the cathode mixture. Plenty of research has reported the coating layer effect in the typical voltage window, while the influence at different voltage windows is unclear. Herein, the degradation mechanism of the bare and LiNbO3 coated LiCoO2 electrodes in all-solid-state batteries when cycled at different cut-off voltages has been systematically investigated. Thecoated electrodes exhibit superior electrochemical performance than the bare electrodes at different charging/discharging rates when the upper cut-off voltage is 3.6 V, while both electrodes show fast degradation of battery performance at higher cut-off voltages (3.9 and 4.2 V). The electrochemical performances are highly dependent on the interfacial stability between the active material and solid electrolyte in the cathode mixture and the structural instability of LiCoO2 at different voltage windows. The evolution of interfacial resistances is systematically investigated in combination of in-situ EIS, relaxation time distribution (DRT), TEM, and XPS. Structural changes of bare and coated LiCoO2 before and after cycled at different cut-off voltages are studied by XRD, TEM, and dQ/dV analysis. The clarification of complex interfaces and phase stability evolution of LiCoO2 provides a strong theoretical basis for constructing high-performance all-solid-state batteries.

Hybrid Halide Solid Electrolytes and Bottom-up Cell Assembly Enable High Voltage Solid-State Lithium Batteries

Interface between halide based solid electrolytes and layered transition metal oxide cathodes has been found to be electro-chemically stable due to stability of chloride compounds, in particular, at >4V range. The extent of interfacial stability is correlated with the type of cationic and anionic species in the solid electrolyte compound, a fact supported by theoretical prediction and yet, not accurately measured in composite cathode mixtures. By altering the architecture of cathode into a dense additive-free structure, we have identified differences in interfacial stability of chloride compounds which are hidden in composite cathode formats. In this work, we report the use of dense cathode to track the electrochemical evolution of interface between a hybrid halide solid electrolyte composed of chloride and fluoride species. Introducing fluoride compounds is known to be a promising method to expand the oxidation stability while the nature of such expansion is found to be related to kinetics rather than thermodynamics, we report. Furthermore, fluorination of solid electrolyte is generally accompanied with loss of ionic conductivity due to strong electronegative fluoride ions. We demonstrate a fundamental change of solid-state battery assembly from conventional electrolyte pelletizing followed by electrode placement, to a bottom-up assembly route starting with dense cathode, thin (<20µm) layer of SE and anode addition, which compensates for the suppressed conductivity of fluorinated halide solid electrolytes. Through extensive characterization, compositional optimization, and electrochemical interfacial analysis, we demonstrate stable cycling of LiCoO2/hybrid halide solid electrolyte up to 4.4V vs. Li. Our findings pave the way for expanding the voltage stability of solid electrolytes without compromising the cell performance due to ionic conductivity overpotential issues.

Engineering high conductive Li7P2S8I via Cl- doping for all-solid-state Li-S batteries workable at different operating temperatures

High ionic conductivity and excellent lithium compatibility for sulfide solid electrolytes are vital to developing solid-state Li-metal batteries with high energy density and safety. Li7P2S8I has attracted significant attention due to its low cost, good stability towards lithium metal, and low annealing temperature. However, the low conductivity compared to liquid electrolyte and poor stability with Li metal at high current density limits its applications in solid-state batteries. In this work, the conductivity of Li7P2S8I is first increased from 1.53 mS/cm to 3.08 mS/cm by Cl- doping. The enhanced ionic conductivity is due to the introduction of S2-/Cl-/I- disorder structure in the structure. Then, the Li-ion conductivity of Li7P2S8I0.5Cl0.5 is enhanced up to 6.67 mS/cm via optimizing the pellet-making pressures and temperatures with the hot-press technique. Because of the superior conductivity, the assembled Li2S-LiI/Li7P2S8I0.5Cl0.5/Li-In battery delivers initial discharge capacities of 1051.0 mAh/g, 1385.0 mAh/g, and 713 mAh/g under 0.13 mAh/cm2 at room temperature, 60 °C, and 0 °C, respectively. Moreover, the capacity contribution of the Li7P2S8I0.5Cl0.5 electrolyte in cathode mixture are unraveled, which shows reversible charge/discharge more than 80 cycles and confirms the extra capacity from the electrolytes in the cathode mixture. The hot-press Li7P2S8I0.5Cl0.5 pellet shows excellent lithium compatibility and dendrite suppression capability, achieving stable lithium plating/stripping up to 280 h at 0.1 mA/cm2. The corresponding 3Li2S-LiI/Li7P2S8I0.5Cl0.5/Li battery delivers an initial discharge capacity of 474 mAh/g at 0.13 mA/cm2 and capacity retention of 83% after 30 cycles. This work provides a promising strategy to explore sulfide electrolytes enabling solid-state Li-Metal battery.

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.