High-energy Rechargeable Lithium Batteries Research Articles

Lithium Bis(fluorosulfonyl)imide for Stabilized Interphases on Conjugated Dicarboxylate Electrode.

Carbonyl-based negative electrodes have received considerable interest in the domain of rechargeable lithium batteries, owing to their superior feasibility in structural design, enhanced energy density, and good environmental sustainability. Among which, lithium terephthalate (LiTPA) has been intensively investigated as a negative electrode material in the past years, in light of its relatively stable discharge plateau at low potentials (ca. 1.0 V vs Li/Li+) and high specific capacity (ca. 290 mAh g-1). However, its cell performances are severely limited owing to the poor quality of the solid-electrolyte-interphase (SEI) layer generated therein. Here, we report the utilization of lithium bis(fluorosulfonyl)imide (LiFSI) as an electrolyte salt for forming a Li-ion permeable SEI layer on the LiTPA electrode and subsequently improving the cyclability and rate performance of the LiTPA-based cells. Our results show that, differing from the reference electrolyte containing the lithium hexafluorophosphate (LiPF6) salt, the electrochemical reductions of the FSI- anions occur prior to the lithiation processes of LiTPA electrode, which is capable of building an inorganic-rich SEI layer containing lithium fluoride (LiF) and lithium sulfate (Li2SO4). Consequently, the lithium metal (Li°)||LiTPA cell shows significantly improved cycling performance than the LiPF6-based reference cell. This work provides useful insight into the reductive processes of the FSI- anions on negative electrodes, which could spur the deployment of highly sustainable and high-energy rechargeable lithium batteries.

High Rate and Low-Temperature Stable Lithium Metal Batteries Enabled by Lithiophilic 3D Cu-CuSn Porous Framework.

Lithium (Li) metal is regarded as the "Holy Grail" of anodes for high-energy rechargeable lithium batteries by virtue of its ultrahigh theoretical specific capacity and the lowest redox potential. However, the Li dendrite impedes the practical application of Li metal anodes. Herein, lithiophilic three-dimensional Cu-CuSn porous framework (3D Cu-CuSn) was fabricated by a vapor phase dealloying strategy via the difference in saturated vapor pressure between different metals and the Kirkendall effect. CuSn alloy sites were converted into LiSn alloy sites through the molten Li infusion method, and composite Li metal anodes (3D Cu-LiSn-Li) are achieved. Alloyed tin, as the bridge between the porous copper substrate and metallic Li, plays a critical role in optimizing Li nucleation and enhancing the fast lithium migration kinetics. This work demonstrates that lithiophilic binary copper alloys are an effective way to achieve room-temperature high rate performance and satisfied low-temperature cycling stability for Li metal batteries.

(Battery Division Research Award) A New Perspective on Layered Transition Metal Oxides As Cathode Active Materials

High energy rechargeable lithium batteries (RLBs) continue to be the most favorite choice for vehicle electrification [1]. Among all cathode active materials, layered transition metal oxides containing nickel (Ni), manganese (Mn), or cobalt (Co), remain the most desired to improve energy density and performance [2]. As the current electrolyte system restricts high voltage operation, new cathode active materials with higher capacity are being sought today. How to seek a better cathode active material needs some better guidance as well. Here, a new perspective on the layered transition metal oxide cathode active materials is proposed based on our recent analysis of the performance characteristics of these current cathode active materials that were evaluated or reported in the literature. This new perspective is supposed to provide a more coherent framework to explain their commonality of the performance in realizing higher capacity within the same stability range. With this perspective, the principle of seeking a better cathode active material could be improved with this understanding.

Next Generation Batteries: Status and Challenges of High Energy Rechargeable Lithium Batteries

Batteries play a critical role in modern society. The electrification of transportation and deep decarbonization of the energy infrastructure require the development and deployment of high energy, low-cost battery materials and technologies. Among the many different battery chemistries investigated, rechargeable batteries using lithium metal anode remain as one of the most feasible approaches for next generation high-performance and low-cost batteries. Here we will discuss and summarize the progresses and status of the research supported by the Battery500 Consortium. The consortium addresses both fundamental level materials and mechanistic problems and cell level integration and manufacturing challenges. The scope includes developing new electrolytes to reduce the side reactions and improve lithium metal deposition/stripping efficiency, improving cathode cycling stability and cathode utilization, understanding and controlling solid electrolyte interfacial reactions, cell design, optimization and validation. The consortium has made significant progress towards high energy cells (>350 Wh kg-1) and stable cycling life (>600 cycles). The research from the consortium also sheds new lights on the degradation and failure mechanisms of high energy lithium cells and the associated the interfacial reactions.

Guided lithium nucleation and growth on lithiophilic tin-decorated copper substrate

Lithium metal is the ultimate anode choice for high energy rechargeable lithium batteries owing to its ultra-high theoretical capacity, however, Li dendrites and low Coulombic efficiency (CE) caused by disordered Li plating restrict its practical application. Herein, we develop an ultrathin Sn-decorated Cu substrate (Sn@Cu) fabricated by an electroless plating method to induce ordered Li nucleation and growth behavior. The lithiophilic Sn interfacial layer is found to play a critical role to lower the Li nucleation over-potential and promote fast Li-migration kinetics, and the underlying mechanism is revealed using the first principle calculations. Accordingly, a dense dendrite-free and Li deposition with large granular morphology is obtained, which significantly improved the CE and cycling performance of Li||Sn@Cu half cells symmetric cells. Symmetric cells using the Li-Sn@Cu electrode display a much-prolonged life span (>1200 h) with low overpotential (∼18 mV) at a high current density of 1 mA cm−2. Moreover, full cells paired with commercial LiFePO4 cathode (1.8 mAh cm−2) deliver enhanced cycling stability (0.5 C, 300 cycles) and excellent rate performance. This work provides a simple and effective way to bring about high efficiency and long lifespan substrates for practical applications.

Designing Versatile Polymers for Lithium-Ion Battery Applications: A Review.

Solid-state electrolytes are a promising family of materials for the next generation of high-energy rechargeable lithium batteries. Polymer electrolytes (PEs) have been widely investigated due to their main advantages, which include easy processability, high safety, good mechanical flexibility, and low weight. This review presents recent scientific advances in the design of versatile polymer-based electrolytes and composite electrolytes, underlining the current limitations and remaining challenges while highlighting their technical accomplishments. The recent advances in PEs as a promising application in structural batteries are also emphasized.

Polyethylene Oxide-Based Solid-State Composite Polymer Electrolytes for Rechargeable Lithium Batteries

Solid-state polymer electrolytes are considered to be the most promising electrolytes for next-generation high-energy rechargeable lithium batteries due to the advantages of high safety, good mecha...

Stable Lithium Deposition Enabled by an Acid-Treated g-C3N4 Interface Layer for a Lithium Metal Anode.

Li metal has been regarded as one of the most promising anode candidates for high-energy rechargeable lithium batteries. Nevertheless, the practical applications of the Li anode have been hampered because of its low Coulombic efficiency and safety hazards. Here, acid-treated g-C3N4 with O- and N-containing groups are coated on Li foil through a facile physical pressing method. The O- and N-containing groups cooperate to rearrange the concentration of Li ions and enhance the Li ion transfer. Hence, the cycle and rate performances of acid-treated g-C3N4-coated Li electrodes are greatly improved in symmetric cells, which show cycling stability over 400 h at 1 mA cm-2 in ester-based electrolytes and over 2100 h in ether-based electrolytes. As for the Li//LiFePO4 full cells, there is a high capacity retention of 80% over 400 cycles at 1 C. The full cells of Li//S in ether-based electrolytes also exhibit a capacity of 520 mA h g-1 after 400 cycles at 1 C.

Concentrated Electrolytes for High-Energy Metallic Li Batteries

Liquid electrolyte plays a key role in commercial lithium batteries to allow conduction of lithium ion between cathode and anode. Traditionally, taking into account the ionic conductivity, viscosity and dissolubility of lithium salt, the salt concentration in most of liquid electrolytes is typically less than 1.2 mol/L. We propose a new class of “Solvent-in-Salt” (SIS) electrolytes with high salt concentration, in which salt holds a dominant position in the lithium ion transport system. It remarkably enhances cyclic and safety performance of the next-generation high-energy rechargeable lithium batteries via an effective suppression of lithium dendrite and shape change of metallic lithium anode. First, when used in lithium-sulfur battery, the power of this electrolyte is further demonstrated that lithium polysulphide dissolution is inhibited, thus overcoming one of the most challengeable technological hurdles: “polysulphide shuttle phenomenon”. Consequently, a Coulombic efficiency nearing 100% and long cycling stability are achieved. Second, when used in lithium-NCA pouch cell, the ca. 3Ah cell exhibits over 150 cycles.

Embedding of Mg-doped V2O5nanoparticles in a carbon matrix to improve their electrochemical properties for high-energy rechargeable lithium batteries

Mg-doped V2O5@carbon spheres prepared using a PMAA microreactor possess improved electrochemical properties within the potential range of 1.5–4.0 V.

Analyses of Charge/Discharge Mechanism of Fe-Containing Li2S-Based Positive Electrode Material Using X-Ray Absorption and Scattering Measurements

1. Introduction Lithium sulfide (Li2S) is one of the promising cathode active materials for high-energy rechargeable lithium batteries because of its high theoretical capacity (ca. 1170 mAh・g-1) [1]. However, this material shows both electronically and ionically resistive property, which gives rise to relatively low electrochemical performance in the cells [2]. Several attempts have been performed to enhance the conductivity of Li2S, such as forming composites with several metals (Li2S-Fe, Li2S-Cu) [1,2] or carbon [3,4]. Recently, we have tried to prepare Fe-containing Li2S-based positive electrode materials (Li8FeS5) and found that the cells showed the discharge capacity of ca. 330 mAh・g-1 and it was enlarged to ca. 730 mAh・g-1after the pre-cycling treatment [5]. However, its charge/discharge mechanism and the effect of the pre-cycling treatment were still unclear. In the present work, we analyzed the structure of Li8FeS5for Li extraction/insertion reactions with/without pre-cycling treatment using X-ray absorption and scattering measurements. 2. Experimental Li2S and FeS with a molar ratio of 4 : 1 were blended thoroughly, and the mixture was then treated by the SPS process at 600oC [5]. The resulting pellet was ground and mixed with carbon (acetylene black) powder with a weight ratio of 9 : 1, and then it was mechanically milled for 8 h to yield the Li8FeS5sample. The obtained Li8FeS5 sample was characterized by X-ray diffraction, as well as inductively coupled plasma (ICP) and atomic absorption spectroscopy. Electrochemical lithium extraction / insertion reactions (charge/discharge) were carried out using lithium coin-type cells with 1M LiPF6 / (EC + DMC) electrolyte at a current density of 46.7 mA・g-1(corresponding to 0.04C) initially with charging with and without stepwise pre-cycling treatment [5]. Fe K-edge X-ray absorption fine structure (XAFS) of the composite cathode materials before and after charge/discharge cycling, sealed in argon filled aluminum laminate bags, were measured using a laboratory-type spectrometer (Technos EXAC-820) and S K-edge XAFS of the materials were measured in vacuum chamber by the beamline BL-10 in SR center of Ritsumeikan University, respectively. We also carried out the X-ray scattering measurements at the beamline BL28XU in SPring-8, and the obtained data were conducted by pair distribution function (PDF) analysis [6]. 3. Results and Discussion The obtained Li8FeS5 sample was black in color, and the XRD pattern showed that it consisted of low-crystalline Li2S (antifluorite structure) [5]. The atomic ratio, estimated by ICP and atomic absorption spectroscopy, was Li : Fe : S = 7.8 : 1.0 : 4.8 [5]. The radial structure functions around S atoms for the Li8FeS5 sample, calculated from EXAFS spectra, showed irreversible changes without pre-cycling treatment, while they showed reversible changes after the pre-cycling treatment. And the radial structure functions around Fe atoms showed that the first neighbor peak shifted to shorter distance and the amplitude decreased significantly after the initial charge without pre-cycling treatment. Although the peak position and the amplitude reversibly changed to the initial ones after the subsequent discharge, actually little change was observed in the second cycling. These are consistent with the charge/discharge performances of the cells, where they showed relatively low initial capacity and very rapid cycle degradation. On the contrary, the reversible shift of the distances and change of amplitudes of the first neighbor peaks were observed for the charge/discharge cycling after the pre-cycling treatment. Such stabilized local structure around Fe atoms for Li extraction/insertion reactions might be assigned to the Fe atoms that occupy partially Li site of low-crystalline Li2S lattice with antifluorite structure, which would be formed during the pre-cycling treatment. Probably it would result in the relatively higher capacity and improved cycle performance of the cells. We also carried out the PDF analyses of the Li8FeS5sample with/without pre-cycling treatment, and the calculated radial distribution functions were compared with those obtained by the EXAFS analyses, which will be presented in the Conference.

Organotrisulfide: A High Capacity Cathode Material for Rechargeable Lithium Batteries.

An organotrisulfide (RSSSR, R is an organic group) has three sulfur atoms which could be involved in multi-electron reduction reactions; therefore it is a promising electrode material for batteries. Herein, we use dimethyl trisulfide (DMTS) as a model compound to study its redox reactions in rechargeable lithium batteries. With the aid of XRD, XPS, and GC-MS analysis, we confirm DMTS could undergo almost a 4 e(-) reduction process in a complete discharge to 1.0 V. The discharge products are primarily LiSCH3 and Li2 S. The lithium cell with DMTS catholyte delivers an initial specific capacity of 720 mAh g(-1) DMTS and retains 82 % of the capacity over 50 cycles at C/10 rate. When the electrolyte/DMTS ratio is 3:1 mL g(-1) , the reversible specific energy for the cell including electrolyte can be 229 Wh kg(-1) . This study shows organotrisulfide is a promising high-capacity cathode material for high-energy rechargeable lithium batteries.

High Capacity Sulfurized Alcohol Composite Positive Electrode Materials Applicable for Li-S Batteries

Introduction Elemental sulfur is one of the promising cathode active materials for high-energy rechargeable lithium batteries because of its high theoretical capacity (ca. 1670 mAh-g-1) and relatively low cost [1]. However, sulfur cathode has some disadvantages, such as low electrical conductivity and dissolution as polysulfides into electrolyte during electrochemical cycling, resulting in shuttling in Li-S batteries. Several attempts have been performed to solve these problems, and the major improvements have been made by forming composites with carbon matrix, whereby sulfur was physically confined in some fine structures [2]. Despite the improved electrical transfer and the suppressed shuttling of polysulfides, these S-C composites cells still showed gradual capacity degradation. This is originated from the low binding energy between sulfur and carbon matrix [3].Another type of S-C composites has been developed, based on the concept of embedding sulfur into a conductive polymer matrix, such as sulfurized poly(acrylonitrile) (S-PAN) [4-6]. In these organosulfur materials, sulfur is thought to be incorporated in cavity of molecular scale, which significantly prevents the dissolution as polysulfides, leading to the excellent cycle stability of the cells. Although many kinds of polymer framework have been investigated, there still remain challenges for exploring the organosulfur materials with higher sulfur contents, using inexpensive and non-toxic reagents [3]. In the present work, we have tried to prepare new type of organosulfur cathode materials using primary alcohol. The structure and the electrochemical properties of the obtained sulfurized alcohol composites (SAC) were examined. Experiments SAC was prepared by refluxing primary alcohol 1-C n H2n+1OH (n = 3 – 10) (1g) and elemental sulfur (5g) in a glass tube equipped in an electric furnace, which was heated at 400oC. After cooling, the resulting powder was ground and then heated again at 300oC under N2 flow in order to eliminate residual elemental sulfur to yield the SAC. We also prepared S-PAN after the method reported previously [7]. The obtained SAC was characterized by XRD, Raman spectroscopy, TEM observation, and elemental analysis, as well as S and C K-edge XAFS measurements (SR Center, Ritsumeikan University). Electrochemical lithium insertion / extraction reactions were carried out at 30oC using lithium coin-type cells with 1M LiPF6 / (EC + DMC) electrolyte at a current density of 30 mA-g-1 between 1.0 and 3.0 V initially with discharging. The electrochemical performances were also examined by assembling all-solid-state cells using the Li2S-P2S5 solid electrolyte and indium anode in a similar manner as described previously [8] at a current density of 30 mA-g-1 between 0.4 and 3.5 V. Results and Discussion The obtained SAC samples were black in color, and the XRD patterns showed no significant peaks, irrespective of the primary alcohol (n-value). High-resolution TEM observations showed no obvious crystalline domains, indicating an amorphous phase. The EDX mapping showed relatively homogeneous distribution of sulfur and carbon in the SAC samples. The elemental analyses indicated that the sulfur content was more than 60 wt%, which was higher than that reported previously for S-PAN (ca. 30 – 53 wt%) [4,5]. The Raman spectra showed some peaks at 480, 1250, 1440cm-1, suggesting the S-S, C-S, and C-C bonds, respectively. Analyses of the D- and G-bands indicated that the C-C bonds mainly consisted of sp3-type configuration, which makes a clear contrast to the S-PAN where the C-C bonds consisted of mainly sp2-configuration.The electrochemical tests for the SAC sample cells showed that the initial discharge capacity was ca. 800 - 1000 mAh-g-1, which was higher than that of S-PAN, due possibly to higher sulfur contents. Also, the all-solid-state cells with the SAC samples showed the discharge capacity of ca. 600 – 800 mAh-g-1. The charge/discharge mechanism was examined using S and C K-edge XAFS measurements, and the results will be presented in the conference. Acknowledgment This work was financially supported partly by “Next-generation storage battery material evaluation technology development” project of NEDO and METI, Japan.

Preparation of Li2s-FeS x -C Composite Positive Electrode Materials and Their Electrochemical Properties with Pre-Cycling Treatment

1. Introduction Lithium sulfide (Li2S) is one of the promising cathode active materials for high-energy rechargeable lithium batteries, because it has a high theoretical capacity (ca. 1170 mAhg-1) and has an advantage that a variety of anode materials without lithium sources are applicable in the practical battery system [1]. However, this material is both electronically and ionically resistive, which gives rise to low active material utilization in the cells [2]. Several attempts have been performed to enhance the conductivity of Li2S, such as forming composites with several metals (Li2S-Fe, Li2S-Cu) [1,2] or carbon [3-5]. Recently, we have tried to prepare the composite with FeS2 (Li2S : FeS2 = 1 : 1 molar ratio) using the spark-plasma-sintering (SPS) process and found that the cells showed the initial charge capacity of ca. 330 mAhg-1 [6]. For improving the charge capacity, preparation of the composite with Li2S-rich composition is required. In the present work, we tried to prepare the Li2S-FeS x -C (x = 1, 2) composites with a Li2S : FeS x = 4 : 1 molar ratio using the combination processes of the SPS and the mechanical milling, and examined their electrochemical properties. 2. Experimental Li2S and FeS2 (or FeS) with a molar ratio of 4 : 1 were mixed thoroughly, and the mixture was then treated by the SPS process [6] at 600oC. The resulting pellet was ground and mixed with carbon (acetylene black) powder with a weight ratio of Li2S-FeS x : C = 9 : 1, and then it was mechanically milled for 8 h to yield the Li2S-FeS x -C composites. All the procedures were carried out in an argon atmosphere, because Li2S is very sensitive to atmospheric moisture. The obtained composite samples were characterized by XRD, as well as Fe and S K-edge XAFS measurements. Electrochemical lithium insertion / extraction reactions were carried out using lithium coin-type cells with 1M LiPF6 / (EC + DMC) electrolyte at a current density of 46.7 mAg-1 (corresponding to 0.04C) initially with charging. For improving the electrochemical performances, we applied pre-cycling treatment to the present Li2S-FeS x -C composite sample cells, whereby cycle capability of some oxide cathode active materials (such as Li(NiCoMn)O2) was successfully improved [7]. 3. Results and Discussion The obtained Li2S-FeS x -C composite samples were black in color, and their XRD patterns showed that they consisted of Li2S (antifluorite structure) with low crystallinity. The atomic ratio, estimated by ICP and atomic absorption spectroscopy, was Li : Fe : S = 7.8 : 1.0 : 4.8 for the Li2S-FeS x -C composite sample with Li2S : FeS = 1 : 4. Since the initial composition was Li : Fe : S = 8 : 1 : 5, this result indicates that negligibly slight amounts of Li and S (ca. 3 – 4%) were lost during the SPS and the following milling processes. The electrochemical tests for the Li2S-FeS x -C sample cells showed that the initial charge capacity was ca. 600 mAhg-1, which was much higher than the previously reported Li2S-FeS2 (1 : 1 molar ratio) sample cells (ca. 330 mAhg-1) [6]. The discharge capacity was ca. 330 mAhg-1 with the normal electrochemical cycling, and it was enlarged to ca. 730 mAhg-1 after the pre-cycling treatment, Fig. 1. This result indicates that the pre-cycling treatment was effective for improving the electrochemical performances of the Li2S-FeS x -C composite cells. Ex-situ XRD measurements showed that the peaks ascribed to Li2S disappeared after the normal electrochemical cycling, while they were still observable after the pre-cycling treatment. Also, ex-situ S K-XAFS measurements showed the reversible changes of the valence states of S atom with the pre-cycling treatment. Therefore, the pre-cycling treatment of the Li2S-FeS x -C sample was effective for maintaining the antifluorite structure, as well as for improving the reversibility of the valence states of S atom, which would be responsible for improving the electrochemical performances of the Li2S-FeS x -C composite sample cells.

A new class of Solvent-in-Salt electrolyte for high-energy rechargeable metallic lithium batteries

Liquid electrolyte plays a key role in commercial lithium-ion batteries to allow conduction of lithium-ion between cathode and anode. Traditionally, taking into account the ionic conductivity, viscosity and dissolubility of lithium salt, the salt concentration in liquid electrolytes is typically less than 1.2 mol l(-1). Here we show a new class of 'Solvent-in-Salt' electrolyte with ultrahigh salt concentration and high lithium-ion transference number (0.73), in which salt holds a dominant position in the lithium-ion transport system. It remarkably enhances cyclic and safety performance of next-generation high-energy rechargeable lithium batteries via an effective suppression of lithium dendrite growth and shape change in the metallic lithium anode. Moreover, when used in lithium-sulphur battery, the advantage of this electrolyte is further demonstrated that lithium polysulphide dissolution is inhibited, thus overcoming one of today's most challenging technological hurdles, the 'polysulphide shuttle phenomenon'. Consequently, a coulombic efficiency nearing 100% and long cycling stability are achieved.