High Energy/Power Density, Safe Lithium Battery with Nonflammable Electrolyte

Titanium dioxide (TiO2), a candidate as anode active material for lithium ion batteries, has attracted much attention from researchers due to its safety characteristics arising from its high electrochemical potential (~1.5V) vs. Li/Li+, low cost, material availability and environmental benignity. However, low electric conductivity, sluggish Li+ diffusivity and poor cycle performance of TiO2 have limited its wide acceptance in practical rechargeable lithium ion batteries. Various strategies such as TiO2-C-nano metal composites [1], nanofibers [2], and TiO2 flakes [3], have been investigated in literature work. While these studies led to improved performance to various degrees, they were limited either in rate (<20C) or cycle life (<100 cycles) or both. A recent work [4] involved atomic layer deposition (ALD) of TiO2on graphene powders and demonstrated vastly improved rate and cycle capabilities of the resulting materials. Here we present an alternative and promising method of preparing extremely high rate and long cycle life anodes via ALD coatings of TiO2on mesoporous activated carbon (AC) electrodes. Figure 1 shows charge and discharge voltages between 1.5V and 3.0V (vs. Li/Li+) of an ALD TiO2-AC and a mesoporous AC baseline coin half cell versus specific capacity based on total active materials. Conventional carbonate-based lithium ion electrolyte was used. The ALD TiO2-AC cell demonstrated nearly five-fold capacity increase against the baseline with voltage profiles typical of nano TiO2. The contribution of ALD TiO2to the observed capacity is ~83%, which leads to ~73 mAh/g specific capacity. The relatively low specific capacity is because of the 1.5V cutoff voltage used in this study. Figure 2 shows rate performance of ALD TiO2-AC vs. AC baseline half cells. The ALD TiO2-AC demonstrated very high rate capability, e.g. delivering 70% of low rate capacity at 400C rate, surpassing that of AC baseline. Figure 3 shows excellent cycle stability of ALD TiO2-AC half cell with 80% capacity retention after 800 cycles. The remarkable electrochemical performance demonstrated from ALD TiO2-AC is attributed to ALD enabled TiO2nano structure. Such nano structure is responsible for facile lithium insertion/extraction leading to extremely high rate capability and long cycle life due to stress/stain free nano architecture. The results in this study suggest a promising material processing methodology for high rate and long cycle life anodes for lithium ion batteries used in applications that require fast rate capability, when implemented with high throughput, high volume ALD processes. Figure 1. Charge and discharge voltage profiles of ALD TiO2-AC/Li vs. AC/Li baseline half cells.Figure 2. Rate capability tests of ALD TiO2-AC/Li vs. AC baseline half cells.Figure 3. Cycle life test of an ALD TiO2-AC/Li cell. References Song Gyun Lee, Honggui Deng, Jun Hu, Lihui Zhou, Honglai Liu, Int. J. Electrochem. Sci., 8, 2204 (2013).Zunxian Yang, Guodong Du, Qing Meng, Zaiping Guo, Xuebin Yu, Zhixin Chen, Tailiang Guo, and Rong Zeng, J. Mater. Chem., 22, 5848 (2012).Ming-Che Yang, Yang-Yao Lee, Bo Xu, Kevin Powers, Ying Shirley Meng, J. Power Sources, 207, 166 (2012).Chunmei Ban, Ming Xie, Xiang Sun, Jonathan J Travis, Gongkai Wang, Hongtao Sun, Anne C Dillon, Jie Lian and Steven M George, Nanotechnology 24, 424002 (2013).

Bipolar-type all-solid-state lithium batteries are expected to maintain higher energy density than that of the conventional stacked lithium-ion battery using organic liquid electrolytes. The main problem of the conventional stacked lithium-ion battery is the leakage of organic liquid electrolytes. Bipolar-type all-solid-state battery is composed of solid-state electrolytes as shown in Figure 1, it is possible to supply a high voltage, avoiding the aforementioned weak point of the conventional stacked lithium-ion battery. Presently, the cases of solid-state electrolytes having sufficient lithium ion conductivity and high stability in the voltage range for battery operation are limited. We reported the fabrication and characterization of quasi-solidified hybrid electrolytes composed of room temperature ionic liquids (RTILs) and 7 nm fumed-silica in our previous study. On the basis of our previous works, the quasi-solidified hybrid electrolytes can be treated as solid-state electrolytes, and it possess liquid-like Li-ion transport properties with high ionic conductivity and high stability. Therefore, the quasi-solid-state hybrid electrolyte is considered as a potential candidate for bipolar-type all-solid-state lithium-ion batteries. In this study, we assembled the bipolar-type all-solid-state Li battery using a quasi-solid-state hybrid electrolyte and the battery performance was investigated.Lithium bis(trifluoromethaesulfonyl)amide (LiTFSA) was dissolved into tetraethylene glycol dimethyl ether (G4) in equimolar ratio to prepare RTIL-like complex solution. The quasi-solid-state electrolyte (QSE) powder was fabricated according to our previously reported method [1]. In this study, we prepared the QSE powder containing 80 vol% of G4/LiTFSA liquid, and a transparent quasi-solid-state hybrid electrolyte sheet was obtained by mixing polytetrafluoroethylene (PTFE) powder with the QSE powder in 5 wt%. The cathode was made by mixing LiFePO4 (theoretical capacity of 170 mAh g-1), AB, QSE powder and PTFE, with a weight ratio of 35:10:45:10. The composite cathode, the QSE sheet and Li metal anode was assembled as one-unit cell. Two and three unit-cells, connected in series, were prepared. The charge-discharge measurements of the one-, two- and three-unit bipolar all-solid-state cells were performed at 35 oC and a rate of 0.1C.The quasi-solid-state hybrid electrolyte was a white powder and the quasi-solid-state electrolyte sheet of 200 mm thickness was prepared [1] and used to assemble all-solid-state cells. The bipolar-type all-solid-state lithium batteries with different stack structures of one-, two- and three-unit cells connected in series in one package were assembled and the battery performances were investigated. The discharge capacity of the one-unit cell reached 161 mAh g-1 at the initial cycle with coulombic efficiency of 99 %. For such one-unit cell, discharge capacity was still maintained at 160 mAh g-1 even after 50 cycles, and the capacity retention was kept 99 %. The discharge capacities of the batteries with two- and three-unit cells were 160 mAh g-1 and 165 mAh g-1, respectively, which were as high as that of one-unit cell. These results implied the cathode utilization ratios of all the bipolar batteries up to 94 %. The coulombic efficiencies for two- and three-unit cells reached 98 % and 99 %, respectively. The discharge plateaus of two- and three-unit cells were observed in the voltage range of 6.7-6.8 V and 10.0-10.2 V, which were twice and three times to the one-unit cell voltage. In summary, these results suggest that our quasi-solid-state electrolytes were successfully applied to the bipolar-type all-solid-state lithium battery.Reference [1] A. Unemoto, T. Matsuo, H. Ogawa, Y. Gambe and I. Honma, J. Power Sources, 244, 354 (2013).

Performance Testing of Lithion 8-Cell, 25 AHr Lithium-Ion Batteries for Future Aerospace Applications

Global demand for lithium-ion secondary batteries have been increasing due to new market growth from electric vehicles and power storage systems. Lithium-ion batteries possess high power density, energy density and long cycle life without memory effect and little self-discharge, and have been primary energy storage system for commercial electronics. However, recent accidents regarding battery safety, such as Samsung Note 7 issue, has raised doubt among public about lithium-ion batteries as option for energy storage. Separator is one of the primary component for lithium-ion battery safety. Commercial separators like PE or PP not only possess outstanding mechanical and electrochemical performance, but also have thermal shutdown function that provide safety measure by pore—blocking with melted polyolefin materials. Nevertheless, polyolefin materials suffered serious shrinkage at elevated temperature, which cause internal short-circuited of batteries ; also, polyolefin materials have relatively low electrolyte uptake, and could be major obstacle for future lithium-ion battery application. Hence it’s necessary to design new type of separator that guarantee battery safety and demonstrate better electrochemical performance In this study, we proposed a brand-new method to design composite separator with high thermal stability, electrolyte uptake ability and thermal shutdown function. Polyimide(PI) nanofiber film was used as substrate and produced by electrospinning technique, and ultra-thin Low-Density-Polyethylene(LDPE) layer was laid upon PI by simple spin-coating method. Spin-coating method provided unique advantages such as ultra thin coating layer (less than 1 micron), uniform coating structure and simple process, and was yet been applied for construction of composite film as lithium-ion battery separator. Coating parameter was tuned to obtain the optimized composite separator. Field-emission scanning electron microscope (FE-SEM) was used to investigate morphologies of separators ; Contact angle measurement was conducted to verify electrolyte affinity of different separators ; A.C. impedance method was used to measure conductivities and verify thermal shutdown of separators, and electrolyte uptake of different separators were measured by electrolyte soaking method in an argon-filled glovebox. The composite film had sub-micron average pore size, and possessed excellent physical properties, for instance, high porosity(73%), electrolyte uptake(1300%), ion conductivity(4.3*10-4 S/cm), air permeability(gurley value=0), and thermal stability(no shrink up to 150。C). Thermal shutdown function of composite film was also confirmed by impedance measurement at elevated temperature. It was noticed that physical properties between pristine PI and composite film were similar owning to ultra-thin coating layer, which mitigate performance loss from LDPE coating. Afterward, full cell battery tests were conducted with CR2032 type coin cell (Cathode : LFP, anode : MCMB, electrolyte : 1 M LiPF6 in EC/EMC/DMC=1:1:1+1%VC, 1C=2.4mAh/g). The first cycle charge-discharge curves, rate capability and cyclic performance were conducted. The composite film showed flatter first cycle charge-discharge plateau, better capacity retention at higher C-rate (Composite film :102 mAh/g at 1C, 79% retention, Celgard 2500 : 73 mAh/g, 51% retention , w.r.t. 0.1C), and higher discharge capacity at 0.5C 50th cyclic test. The higher porosity and electrolyte uptake of composite film facilitated ion conduction and were the main cause for enhanced battery performance. With enhanced thermal stability and electrochemical performance, we expected this type of composite separator to be promising for future lithium-ion battery application. Figure 1

State-of-the-art (SOA) Li-ion batteries (e.g., with graphite anode and LiCoO2 cathode) for consumer electronic devices (e.g., cell phones, laptops) are designed to operate at a certain voltage range, e.g., 3-4.2V [1]. When an electronic device, like a cell phone, indicates “low battery”, the battery is near its low operating voltage threshold, and soon the device may automatically shut down to prevent the battery from further use (discharge). If a SOA Li-ion battery is allowed to further discharge to a very low cell voltage, e.g., near 0V, the battery will deteriorate quickly, manifested with a reduced battery capacity (electric charge, Ah), i.e., reduced battery use time. This is because, at or near 0V, the anode potential can exceed the substrate (commonly Cu) dissolution potential, which results in corrosion of the Cu substrate (pittings, holes) leading to compromised battery performance [2]. A battery capable of 0V (or near 0V) storage is desirable as it overcomes irreversible battery performance losses from self-discharge (to a very low voltage). For this reason, SOA Li-ion batteries are maintained above a certain threshold, e.g. > 20-30% capacity. For large format Li-ion batteries/packs, the energy left inside batteries at storage can cause serious concerns regarding: (i) safe battery transport, (ii) high maintenance cost (monitoring and periodically charging the batteries) and (iii) safe battery storage. Li-ion battery safety is a real issue exemplified by the recent Boeing 787 battery [3].Prior art to remedy Li-ion battery at or near 0V storage includes the use of an anode substrate with a higher dissolution potential, e.g., Ti substrate [4]. However Ti current collectors possess shortcomings including high cost of the Ti current collector and poor electrode coating adhesion on Ti substrate. Moreover, fundamentally, for a graphite-based anode, a solid-electrolyte-interface (SEI) film formed on graphite anode (due to organic electrolyte reduction) can break down at or near 0V and adversely impact battery performance and life. Here we present a novel approach to develop a high performance Li-ion battery, capable of deep discharge and/or storage near 0V. Our anode active material selection criterions include: (i) amenable to substrates with high dissolution potentials, (ii) sufficient (electrical) potential to avoid SEI film formation and (iii) high specific capacity for battery high energy density. Our cathode active material selection criterions include high specific capacity and high voltage to achieve high battery specific energy. Other criterions common to the anode and the cathode include high rate capability and robust cycle life. Figure 1 shows cell capacity retention as a function of cycle number for ADA near 0V capable Li-ion cells. The cells were stored at ~ 0V for 2 days for every 5 cycles. The control cell was cycled without low voltage storage. After accumulative storage for 30 days at 50mV and 100mV, respectively, the ADA near 0V capable cells demonstrated little or no capacity fade, comparable to the control cell. We attribute the excellent cell deep discharge/storage resilience to our near 0V tolerant electrode material selections. For comparison purposes, we applied the identical test conditions to graphite based Li-ion cells as shown in Figure 2. The graphite based Li-ion cells experienced rapid capacity deterioration (i.e., capacity drop to zero) after a short period of ~ 0V storage. This is likely due to Cu current collector dissolution and dissolution/reformation of SEI films on graphite anode.Our study showed that this battery technology is a very promising high performance and safe power source capable of long-term ~ 0V deep discharge/storage. This battery technology is being developed for applications in the transportation, consumer electronics, military and space markets. References "Lithium Ion technical handbook". Gold Peak Industries Ltd. November 2003. Rui Guo, Languang Lu, Minggao Ouyang, and Xuning Feng, Scientific Report, 2016; 6: 30248. National Transportation Safety Board Report, Case No. DCA131A037, March 7, 2013. Hisashi Tsukamoto, Clay Kishiyama, Mikito Nagata, Hiroshi Nakahara, Tiehua Piao, US6596439. Figure 1

The application of lithium-ion batteries to long-range electric automobiles requires negative electrode materials with a higher specific capacity than traditional graphite. Next-generation materials should have both a high gravimetric capacity and capacity retention upon cycling. Silicon is a promising material for the negative electrode as it has a theoretical capacity nearly 10 times greater than graphite (3579 mAh/g for Li15Si4) (1). However, pure silicon (Si) undergoes severe mechanical stresses and pulverization during lithiation and delithiation (2). In contrast, Li4Ti5O12 (LTO) is mechanically stable and has a high rate capability. This makes it suitable to buffer the volumetric expansion of silicon when integrated into a core/shell design. In this study, a facile sol-gel technique was used to treat silicon nanoparticles and create a Si-core @ LTO-shell by modifying a procedure described previously (3). These silicon nanoparticles retain the high capacity associated with Li-Si alloys, but the pulverization of the particles is reduced. Further improvement to the cycle stability of the Si/LTO composite was achieved with the addition of graphite to the electrode material. The graphite not only provides capacity, but it is highly stable and helps buffer some of the volumetric expansion of the silicon-rich electrode material (2). The combination of graphite (G) and nano silicon/LTO (Si@LTO) is therefore an economical and scalable approach to increase the energy density of lithium-ion batteries.The electrode composites were tested in half cells and were cycled at C/10 and 1C. The cycling performance of Si@LTO + G revealed an initial high capacity (~860 mAh/g at C/10 and ~650 mAh/g at 1C) and good capacity retention (~75% after 90 cycles at 1C). In contrast, a silicon/graphite (Si/G) composite retained only 35% of its capacity at 1C under the same conditions. Compared to Si/G, the Si@LTO + G composites had lower capacity fade by reducing both silicon pulverization and SEI formation. This was confirmed by a reduction in the impedance of the Si@LTO + G batteries after cycling. Figure 1 illustrates the difference in cycle performance between Si/G and Si@LTO + G electrodes. The Si@LTO + G composite had a better rate capability when the charging rate was increased from C/10 to 1C. At 1C, the Si/G composite immediately lost 50% of its capacity. In contrast, the Si@LTO + G composite immediately lost only 25% of its capacity. This value is similar to the capacity retention of a graphite half cell tested under the same conditions (~372 mAh/g at C/10 and ~280 mAh/g at 1C). The electrode powders were characterized with X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), and Transmission Electron Microscopy (TEM). XRD of the raw Si@LTO powder revealed the presence of crystalline silicon and Li4Ti5O12. The core-shell structure was confirmed with TEM, and EDX revealed a uniformed distribution of the silicon, titanium, and oxygen. The coin cells were characterized with operando XRD using a modified coin cell and coin cell holder designed in-house. This technique was used to observe changes in the phases of the graphite, silicon, and LTO shell. These silicon@LTO + graphite composites prove to be promising for the development of stable and high-energy-density lithium-ion batteries. Figure 1: (a) Normalized delithiation capacity vs. cycle number for both silicon/graphite and core-shell silicon@LTO with graphite. First 10 cycles at a charging rate of C/10, followed by 90 cycles at 1C. (b) Animation of a silicon particle (top) and an ideal Si@LTO particle (bottom) upon lithiation.

As an anode active material for lithium ion (Li-ion) batteries, titanium dioxide (TiO2) has recently attracted much attention from researchers due to its high theoretical specific capacity, safety characteristics arising from its high electrochemical potential (~1.5V) vs. Li/Li+, low cost, material availability and environmental benignity. However, the low electronic conductivity, sluggish Li+ diffusivity and poor cycle performance of TiO2 have limited its widespread acceptance in practical rechargeable Li-ion batteries. Here, we present a promising method of preparing TiO2 based anodes via atomic layer deposition (ALD) coatings of TiO2 on mesoporous activated carbon (AC) electrodes. TiO2-AC anodes prepared in this study demonstrated remarkable electrochemical performance with drastically increased specific capacity, extremely high rate capability attributed to facile Li+ insertion/extraction of ALD coated, nano-sized TiO2 particles, and excellent cycle performance.

Room temperature ionic liquids (RTILs) are desirable electrolyte materials for advanced batteries because of their unique properties such as non-volatility, non-flammability and high thermal and electrochemical stability. We have reported that glyme-Li salt complexes, comprising equimolar mixtures of a glyme (CH3O(CH2CH2O) n CH3) and a Li salt, have similar properties to RTILs and classified as solvate ionic liquids. Certain glyme-Li salt complexes such as lithium bis(trifluoromethylsulfonyl)amide (Li[TFSA]) and tetraglyme (G4) or triglyme (G3) are liquid at room temperature and show high thermal stability, high lithium ion transference number, and high lithium ion concentration. We demonstrated reversible charge-discharge of lithium secondary batteries using glyme-Li salt complex as an electrolyte. Recently, the similar results were obtained with equimolar mixtures of pentaglyme (G5) and Na[TFSA] abbreviated as [Na(G5)1][TFSA] was able to use as an electrolyte of sodium secondary battery. Elemental sulfur has been studied as the post-lithium ion battery cathode material for its high theoretical capacity of 1672 mAh g-1. However, the major drawback of this material is the poor cycle stability because of dissolution of lithium polysulfides into typical organic electrolyte. One facile approach to overcome this problem is trapping the sulfur inside a polymer network such as poly(acrylonitrile) (PAN) to prevent the dissolution. By mixing PAN and excess amount of sulfur and heating at around 300 °C, cyclization and dehydrogenation of PAN is promoted by sulfur and results in sulfur contained p-conjugated polymer (PAN-S). The PAN-S has been studied as cathode active material with high specific capacity, good efficiency and cycling stability. However, most reports of PAN-S dealt with lithium batteries and not so many reports have been done in PAN-S sodium system. In this study, we tested the charge-discharge property of PAN-S composite cathode with [Na(G5)1][TFSA] electrolyte at 30 °C. The PAN-S was synthesized by mixing PAN and elemental surfur in 1:4 weight ratio and heated at 350 °C for 6 hours under Ar atmosphere. The composite cathode was fabricated by mixing PAN-S, AB, PVA in the weight ratio of 70:20:10 with NMP used as homogenizer to obtain slurry and pasted onto Al sheet. The electrolyte was prepared by mixing pentaglyme (G5) and sodium bis(trifluoromethylsulfonyl)amide (Na[TFSA]) in 1:1 molar ratio ([Na(G5)1][TFSA]) and mixed with a hydrofluoroether (HFE) in 1:4 molar ratio in order to improve ionic conductivity. Anode material Na15Sn4was prepared by mixing sodium metal and Sn powder in 15:4 molar ratio by ball mill for 5 hours, 510 rpm. The result of charge discharge test is shown in the figure. The initial discharge capacity was about 500 mA h g(PANS) -1 and charge-discharge capacity after that was around 400 mA h g(PANS) -1with excellent coulombic efficiency for 30 cycles. Although there are capacity decrease as the cycle number increase, the cycle stability is much improved compared to that of elemental sulfur composite cathode and sodium metal anode system.ReferencesT.Tamura et al., Chem. Lett., 2010, 39, 753.K.Yoshida et al.,J. Am. Chem. Soc., 2011, 133, 13121.X. Yu et al., J. Electroanal. Chem., 2004, 573,121-128

The increased global energy demand and pollution of environment due to the consumption of fossil fuels require utilization of energy generated from renewable energy sources such as wind, tidal and solar power. As the contribution of these energy resources grows the energy storage systems with high energy densities, efficiencies and long cycle life become increasingly important. Energy storage systems are needed at times of high energy demand by storing energy when in excess. In this regard supercapacitors (SCs) are considered as the most promising energy storage devices due to their high power density, short characteristic time constant, excellent coulombic reversibility (98% or higher), high energy efficiency (92 – 94%), long cycle life (over 106 cycles) and wide operation temperature range [1-3]. Porous carbon materials are the most promising electrode materials for portable SCs due to the high surface area, good electrical conductivity, good chemical stability, low gravimetric density and low cost [4,5]. The electrical energy accumulated in SCs depends on the electrochemically active surface area and, thus, on the porosity and hierarchical porous structure of a carbon material. In addition, the presence of mesopores in porous carbon materials determines the power density of SCs having a strong effect on the rate of mass transfer and adsorption rate of charge carriers inside the hierarchical porous matrix. Therefore, the characteristics of micro- and mesoporous carbon materials (especially the ratio of micropore and mesopore surface areas and pore volumes) have to be optimized to improve further the specific energy and power density of EDLCs [4,5]. The objective of this study was to investigate the applicability limits of carbon material derived from granulated white sugar (GWS carbon) by hydrothermal carbonization (HTC) method combined with subsequent zinc chloride activation step of hydrochar, for SC electrodes. Synthesized GWS carbon material was used as an electrode material in SC cell filled with 1 M triethylmethylammonium tetrafluoroborate (TEMABF4) solution in acetonitrile (AN) or 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid (EMImBF4) as the electrolytes. Cyclic voltammetry (CV), constant current charge/discharge (CC), electrochemical impedance spectroscopy (EIS) and constant power discharge (CP) methods were used to study the electrochemical performance of EDLC. The EIS, CV and CC measurement results show that the values of specific capacitance are somewhat higher for EMImBF4 (135 F g-1) electrolyte compared to the TEMABF4 in AN (110 F g-1). The CP test results show that at low constant power values the stored energy is higher for EDLC based on EMImBF4 ionic liquid (48 W h kg-1) compared with EDLC based on TEMABF4 in AN electrolyte (39 W h kg-1). However, the best capacitance retention, shortest relaxation time constant and substantially higher energy density delivered at higher constant power values were established for SC cell in 1 M TEMABF4 solution in AN due to the lower viscosity and higher electrical conductivity compared to the ionic liquid based electrolyte [5]. Acknowledgements This research was supported by the EU through the European Regional Development Fund (Centers of Excellence, 2014-2020.4.01.15-0011 and 3.2.0101–0030, TeRa project SLOKT12026T. Higher education specialization stipends in smart specialization growth areas 2014-2020.4.02.16-0026) and Institutional Research Grant IUT20–13. This work was partially supported by Estonian Research Council grants PUT1033 and PUT55.

Surface Stabilization of O3-type Layered Oxide Cathode to Protect the Anode of Sodium Ion Batteries for Superior Lifespan.

Interconnected MoO2/MoS2@NC nanosheets as anodes with high-rate and long-life for lithium-ion and sodium-ion batteries

Atomic layer deposition of ZnO on Li1.3Al0.3Ti1.7(PO4)3 enables its application in all solid-state lithium batteries

With increasing demands for safe, high capacity energy storage to support personal electronics, newer devices such as unmanned aerial vehicles, as well as the commercialization of electric vehicles, current energy storage technologies are facing increased challenges. Although alternative batteries have been intensively investigated, lithium (Li) batteries are still recognized as the preferred energy storage solution for the consumer electronics markets and next generation automobiles. However, the commercialized Li batteries still have disadvantages, such as low capacities, potential safety issues, and unfavorable cycling life. Therefore, the design and development of electromaterials toward high-energy-density, long-life-span Li batteries with improved safety is a focus for researchers in the field of energy materials. Herein, recent advances in the development of novel organic electrolytes are summarized toward solid-state Li batteries with higher energy density and improved safety. On the basis of new insights into ionic conduction and design principles of organic-based solid-state electrolytes, specific strategies toward developing these electrolytes for Li metal anodes, high-energy-density cathode materials (e.g., high voltage materials), as well as the optimization of cathode formulations are outlined. Finally, prospects for next generation solid-state electrolytes are also proposed.

Magnesium anode batteries: Batteries with pure Mg metal anodes have been noted as being potential post Li-ion technologies for the following reasons: -Mg holds almost 6 times the specific energy of LiC6 -Mg is cheaper than Li -Mg is a safer material than Li Despite the clear motivation for assembling Mg batteries, their shortfall to date has been in large part due to the fact that conventional Mg electrolytes are simply not compatible with reversible Mg electrodeposition and dissolution. Electrolytes providing a reversible Mg2+/Mg0 couple: Families of Mg electrolytes known to give reversible deposition and dissolution of Mg include RMgX, Mg(BR4)2, Rm,,(RO)mMgX2-m + AX3-nR’n (A=Al,B; X=F,Cl,Br; R=alkyl or aryl group). Unfortunately, these materials have not found commercial success primarily due to issues with one or more of the following: low anodic stability, low conductivity, low cycling efficiency, corrosiveness, difficulty with production on a large scale, high nucleophilicity, and or lack of compatible cathode materials. The reader is referred to the literature to understand specific drawbacks for each species.1,2 The Case for Room Temperature Ionic Liquids (RTILs): In recent years, ionic liquids have generated a lot of excitement in several branches of science, one of them being energy storage. To date, use of ionic liquid media for Mg electrochemistry has been met with very limited success. There have been claims of reversible Mg deposition and dissolution using conventional Mg salts in RTILs but not without considerable subsequent criticism.3,4It may be that RTILs simply cannot provide an appropriate environment, however, we feel as though they may be overlooked and are more compatible than previously suggested. The obvious benefits from using RTILs in batteries are the following general physical properties: Non-volatileHigh Thermal stability and liquid rangeIntrinsically conductiveWide electrochemical windows The first two characteristics allow us to create extremely dry and inert environments by performing electrochemistry under vacuum as well as high temperatures. In such conditions (0.4mTorr, 100°C) we show moderate stripping behavior, not observed under normal inert gas atmospheres (fig 1 black curve). Furthermore, we believe there are interesting lessons to be learned from work being done with Li and Zn batteries using RTIL solvents. Specifically, double layer structures and solvation environments behave much differently in RTILs than in conventional solvents and have been shown to drastically alter the electrochemical response. For instance, the voltammograms in figure 1 with Zn and Mg salts show unusual cathodic current dips possibly due to a compact ion double layer changing as the potential is swept. See Figure 1:Comparison of Mg, Zn, & Li-TFSI electrolyte solutions in BMPTFSI (~0.1M). We will here present the challenges faced with using Mg electrolytes in RTILs and the possible strategies for using them to create an environment capable of providing facile, reversible Mg/Mg2+electrochemistry. Acknowledgment We acknowledge support from the Army Research Office grant number W911NF-11-1-0432.

In the past decades, due to an always more electrification and the research of a greener environment, Li-ion Batteries (LIB) have taken an important place in worldwide research. Solid-state batteries (SSBs) have the potential to revolutionize the energy storage industry, offering superior safety and energy density in comparison to traditional LIBs[1, 2]. Our research aims to enhance the performance and safety of solid-state batteries at ambient temperature by incorporating electrodes with high specific capacity with a lithium lanthanum zirconate (LLZO) solid electrolyte.The integration of SiNW electrodes into the solid-state battery architecture offers several advantages. SiNWs are known for their large surface area and superior electrical conductivity and offer a strong platform for efficient lithium-ion transport and cell energy density optimization, theoretically almost 10 times the capacity of graphite[3, 4]. Furthermore, LLZO solid electrolytes are a stable and non-flammable alternative to conventional liquid electrolytes[2, 5], significantly improving battery safety.The main objectives of this study are to investigate the combined effects of silicon nanowires (SiNWs) electrodes and LLZO solid electrolyte and to determine the optimal amount of liquid electrolytes to improve cell safety.In this work, an LLZO thin solid electrolyte tape has been manufactured by casting technique. Precise volumes of liquid electrolyte have been added to the LLZO tape to improve surface contact and ion conductivity. Furthermore, the study will provide a view of the relationship between the quantity of liquid electrolytes introduced and their impact on cell stability and safety.Preliminary results show the preparation of a mechanically stable LLZO tape with high ionic conductivity (>10-4 S cm-1) through an easy and up-scalable procedure. Improvements have been reported in the electrochemical performance of SiNW-LLZO solid-state batteries compared to the relative Li-ion liquid cell.In conclusion, here we developed a new thin solid electrolyte tape with high ionic conductivity, used in solid-state LIBs with silicon nanowires as anode material. Moreover, we standardized a procedure to optimize the use of organic liquid electrolytes as an additive, without omitting the volume or using any excess that could lead to safety issues. This optimization process can contribute to the development of solid-state batteries that are not only high-performance but also safe and reliable for various applications, including electric vehicles and portable electronics. References Wu, F., J. Maier, and Y. Yu, Guidelines and trends for next-generation rechargeable lithium and lithium-ion batteries. Chem Soc Rev, 2020. 49(5): p. 1569-1614.Wang, C., et al., Garnet-Type Solid-State Electrolytes: Materials, Interfaces, and Batteries. Chem Rev, 2020. 120(10): p. 4257-4300.Chan, C.K., et al., High-performance lithium battery anodes using silicon nanowires. Nat Nanotechnol, 2008. 3(1): p. 31-5.Kennedy, T., M. Brandon, and K.M. Ryan, Advances in the Application of Silicon and Germanium Nanowires for High-Performance Lithium-Ion Batteries. Adv Mater, 2016. 28(27): p. 5696-704.Xu, L., et al., Garnet Solid Electrolyte for Advanced All ‐Solid ‐State Li Batteries. Advanced Energy Materials, 2020. 11(2).