Reversible Nano Crystalline-Phase Transformation in Si-Based Anode Enables Stable All-Solid-State Batteries.

Fast development of portable electronic devices (such as a smart phone, iPad, and Galaxy Note) and electrified vehicles (such as EVs and HEVs) require better and smaller lithium ion batteries as their energy storages. What is needed for the cathode of the lithium ion battery is a material capable of a higher volumetric energy density as well as gravimetric energy density. However, not only the development of cathode material but also the commercialization of high energy density anode material has been limited due to cathode material’s much lower energy density compared to anode material. In this regard, Li-rich material (Li2MnO3-LiMO2, M=Ni, Mn and Co) that has 150 % higher energy density than commercialized LiCoO2 is the unique next generation cathode material to solve the problem of cathode material’s low energy density. In the past decade, many researches have focused on the surface stabilization method of this material to improve its intrinsic problems of poor cycle/ rate capability and such surface treatment methods have been demonstrated in a few examples, including AlF3 coating and spinel heterostructures, yielding noticeable improvements in rate and cycle ability. Although such surface treatments showed improved rate and cycle performances, achieving the high volumetric energy density and long-term cycle life which are more critical factors for the commercialization of Li-rich material still remained unsatisfied. In general, Li-rich material’s reversible capacity is related with its particle size since the Li2MnO3 phase in large Li-rich material, which is a major component to realize high energy density, is not fully activated in low voltage range below 4.6 V. For this reason, many previous papers reported their results with only small primary particle size below 100nm. The high surface area induced by the small particle size increases side reactions with electrolyte resulting poor long-term cycle life as well as lowers the volumetric energy density. Note that Li-rich material’s deteriorations are generated from its surface and continue to affect its cycling capability and the deteriorations can be divided into two mechanisms: one is side reactions with electrolyte, and another is the phase collapse. The side reactions with electrolyte at its high working voltage yield active material attack speiceses such as HF and electrolyte exhaustion causing Li-rich material’s fast discharge capacity decay during cycles. Furthurmore, it is hardly show long-term cycle life with over 200 cycles since the phase transition from layered structure to spinel-like and NiO rock salt is generated on the surface of active material, and followed by expention of this transition into the bulk. For instance, AlF3 coated Li-rich LNCMO has abrupt capacity fade after 100 cycles, although it showed good rate and cycle capability within 100 cycles. Hence, new active material design, rather than simple surface modification methods such as coating or doping, is required to solve above previous limits.The new material design needs to start with a simple question: how to minimize the damages of surface deteriorations such as side reasction with electrolyte and phase trasnsition on bulk material and maximize volumetric energy density. The most effective solution for the question is increasing the primary particle size with the stable activation method, since the volumetric energy density of cathode material is maximized from synthesis of micron secondary particles consisted of primary particles by using co-precipitation method in industry. Here we demonstrate a novel approach for lithium storage, which is a material design of a secondary structure which consists of large flake shaped primary particle (hundred nanometers x mictrometers) with a novel activation method using simple chemical treatment to achieve superior long-term cycle life with high volumetric energy density. In this design, the large primary particle effectively reduced its surface area producing markedly decreased surface instability reaction as well as high tap density. Interstingly, the chemical approach activated only surface Li2MnO3 phase of large primary particle and the very surface activation effectively overcame the activation problem, which is limit of large primary particle have. This novel concept is very meaningful in that it is the first and unique method to achieve cathode material’s high volumetric energy density with long-term cycle life. As a result, this novel designed material affords remarkable battery performance with extremely high cycle retention during 400 cycles and high volumetric energy density ever reported before.

Water-in-salt electrolyte Zn/LiFePO4 batteries

: The objective of this ONR program is to develop fundamental understanding on the material requirement of dielectric polymers in order to achieve high energy density with low loss and high dielectric strength. On the material front, the objective is to design and develop dielectric polymers of high energy density and low losses for pulse power applications. In the past three years, we have developed and investigated dielectric polymers with strongly coupled dipoles (modified PVDF based polymers) and their blends to achieve these objectives. Built upon the success of the polar-fluoropolymers, we have investigated a series of high temperature dielectrics with molecular units of high dipole moment and developed new class of polymer dielectrics based on aromatic polythiourea (ArPTU), which is capable of maintaining its low dielectric loss (high electric charge-discharge energy efficiency 90%) up to an ultra high operation fields ( 1 GV/m) with a very high electric energy density ( 24 J/cm3). To develop understanding of the molecular and nano-structure mechanisms, a systematic dielectric studies, including the thermal stimulated discharge current (TSDC) measurement, have been carried out. It was shown that it is the deep traps with high activation energy and large trap density in the PTU thin films that are responsible for the observed low conduction loss and high dielectric strength. Trap-limited high field conduction was studied by the electron hopping theory in the amorphous material.

Developing dielectric capacitors with both a high power density and a high energy density for application in power electronics has been a long-standing challenge. Glass-ceramics offer the potential of retaining the high relative permittivity of ceramics and at the same time of exhibiting the high dielectric breakdown strength and fast charge/discharge rate of glasses, thus producing concurrently high power and energy densities in a single material. In this work, glass-ceramics are fabricated to achieve simultaneously high power and energy densities, high efficiency, and thermal stability by tuning the glass crystallization process via a suitable nucleating agent and a high oxygen partial pressure. Under the same practical charge-discharge test conditions, the as-prepared glass-ceramics combine the high energy density of ceramics and ultrafast discharge rate of glasses, producing the highest power density among glass- and ceramic-based dielectric materials. This work demonstrates the significant potential of achieving both high power and energy densities in glass-ceramics by optimizing the glass crystallization process.

Li ion battery (LIB) and electrochemical capacitor (EC) are considered as the most widely used energy storage systems (ESSs) because they can produce a high energy density or a high power density, but it is a huge challenge to achieve both the demands of a high energy density as well as a high power density on their own. A new hybrid Li ion capacitor (HyLIC), which combines the advantages of LIB and Li ion capacitor (LIC), is proposed. This device can successfully realize a potential match between LIB and LIC and can avoid the excessive depletion of electrolyte during the charge process. The galvanostatic charge-discharge cycling tests reveal that at low current, the HyLIC exhibits a high energy density, while at high current, it demonstrates a high power density. Ragone plot confirms that this device can make a synergetic balance between energy and power and achieve a highest energy density in the power density range of 80 to 300 W kg−1. The cycle life test proves that HyLIC exhibits a good cycle life and an excellent coulombic efficiency. The present study shows that HyLIC, which is capable of achieving a high energy density, a long cycle life and an excellent power density, has the potential to achieve the winning combination of a high energy and power density.

As a promising cathode material for Li-ion batteries(LIBs), Li-rich layered oxide (donated as LLO) has been deeply concerned because of the superior performance and high energy density, however, it’s still suffering from structure deterioration during cycling and the irreversible removal of Li+ in the initial cycle. Micron-sized spherical powders are mainly used as cathode materials due to the high tap density and volumetric energy density, through the spray-drying process can prepare the ideal morphology for LIBs. In this work, hierarchical nano/micro-sphere Li1.2Ni0.13Mn0.54Co0.13O2 composites were synthesized by a two-step spray-dry method by using acetate materials and citric acid as a chelating agent in different molar ratios (transition metal ions (TM): citric acid = 3:1 / 3:2 / 3:3). Adding the CA chelating agent is beneficial to uniform distribution transition metal ions, better structural stability and electrochemical performance of the as-prepared lithium-rich materials. As the results, the morphology of Li1.2Ni0.13Mn0.54Co0.13O2 is spherical and without aggregation occurred. The LLO with hierarchical nano/micro-sphere plays an important role in improving the coulombic efficiency in the first cycle and also enhance the capacity retention after cycling. After 3 cycles activation from 2~4.8V, the discharge capacities of the Li-rich composite samples with 3:1, 3:2, 3:3 ratios displayed 254mAh/g, 280mAh/g, and 267mAh/g, respectively. It was found that the discharge capacity of the LLO composite with the ratio = 3:2 shows the best electrochemical performance among samples. Keywords: Li-ion battery, Cathode material, Li-rich oxide, Spray-Dry, Hierarchical nano/micro-sphere

The mostly widely used lithium (Li) batteries, including lithium-ion (Li-ion) batteries, are activated via organic solvent based electrolytes that are highly flammable. The flammable electrolyte can potentially impose impediments to large-format battery device implementation because, under abuse conditions (e.g., internal short circuit, overcharge, crush, etc.), Li batteries can be hazardous due to heat generation which can potentially lead to toxic/flammable material release, fire and over-pressurization/explosion [1]. These hazards represent major concerns for power source platforms populated by personnel, sensitive equipment and/or vital structures. Recent high-profile incidents involving energy dense batteries (e.g., the Boeing 787 Dreamliner battery fire incident [2]) have increased public awareness of battery safety and resulted in intensified scrutiny for the processes used to develop, manufacture, certify and transport Li batteries. Here we present ADA efforts in the development of a Li battery technology comprised from a nonflammable, high performance, room temperature ionic liquid (RTIL)-based or hydrofluoroether (HFE)-based electrolytes and a nano-engineered, atomic layer deposition (ALD) functional material coated, high voltage, high energy density cathode (i.e., high voltage LiCoO2 or HV-LCO). We demonstrate that such combinations can afford a Li battery technology with an unprecedented high energy density (over state-of-the-art Li-ion or Li batteries), high rate capability, a wide operation temperature range, long cycle life at room temperature (RT) and temperature extremes and safety. Figure 1 shows electrolyte flammability test results. A lighter was used to ignite the electrolyte in a watch glass dish in open air. An organic solvent based, Li-ion battery baseline (conventional) electrolyte was ignited and self-burning when the ignitor was moved away. Each of the RTIL- and HFE-based electrolytes did not ignite and, no self-combustion was observed. Figure 2 shows discharge voltage profiles of Li/HV-LCO cells with RTIL- and HFE-based nonflammable electrolytes as a function of temperature. The cells were cycled between 3-4.6V. At RT, the cells delivered a high specific capacity/energy (> 200 mAh/g and > 800 Wh/kg, cathode active weight). At 50°C, the cells delivered a slightly higher (1-3%) specific capacity than RT. At -20°C, the cells were cycled at C/10 rate and delivered ~75% of the capacity at RT (~155 mAh/g). At -40°C, the cells were cycled at C/20 rate. The HFE-based electrolyte cell delivered a much higher specific capacity (66.5 mAh/g) than the RTIL-based (negligible). Figure 3 shows excellent rate capability of the RTIL-based electrolyte with 85% capacity retention at 10C rate. Figure 4(a) shows high voltage cycle life between 3-4.6V at RT for pristine LCO and HV-LCO based Li cells using the RTIL-based electrolyte. The pristine LCO cells experienced a rapid capacity fade while the HV-LCO cells demonstrated excellent cycle life stability with > 92% capacity retention after 100 cycles. We attribute the excellent HV-LCO high voltage cycle performance to the ALD functional material coating on LCO; this coating effectively suppresses the degradation root cause, i.e., the Co4+ dissolution and hexagonal to monoclinic phase transition [3]. We also evaluated cycle life at an extreme high temperature of 75°C. Figure 4(b) shows high voltage cycle life test data for pristine LCO and HV-LCO based lithium cells using RTIL-based electrolyte with additives. The cells were cycled between 3-4.5V. The pristine LCO based cell still faded much more quickly than the HV-LCO based cell; the latter exhibited an extraordinary high voltage high temperature cycle resiliency (97% capacity retention after 30 cycles, vs. 75% of the pristine LCO) even at the extreme high temperature of 75°C. We attribute the outstanding cycle stability at 75°C to the synergistic benefits of nano-engineered cathode and passivation protection from the electrolyte additives. Our study highlights the importance of combining high performance, safe electrolyte with nano-engineered cathode (e.g., ALD nano-engineered LCO) to render the resultant lithium battery with unprecedented energy density (gained from the high voltage operation), high rate capability, safety (nonflammability) and robust cycle life over a wide temperature range particularly at the extreme high temperatures (e.g., 75°C). We demonstrate that our Li battery technology is ideally suited for many high energy density and safety demanding applications, such as, electric drive vehicles, consumer electronics, medical, space and military applications. References Peter Roth and Christopher J. Orendorff, Electrochem. Soc. Interface, Summer 2012, page 44.“FAA Grounds Boeing 787 Dreamliner for Battery Problems”, Aviation International News, January 2013Akira Yano, Masahiro Shikano, Atsushi Ueda, Hikari Sakaebe, and Zempachi Ogumi, Electrochem. Soc., 164, A6116 (2017). Figure 1

A hybrid PEMFC/supercapacitor device with high energy and power densities based on reduced graphene oxide/Nafion/Pt electrode

The lithium-sulfur (Li-S) battery is one of the most promising candidates of next-generation rechargeable batteries, due to its high theoretical energy density and low production material cost. However, its practical application is hindered by several challenges such as limited energy power density, short cycle life, and low energy efficiency due to the dissolution of intermediate lithium polysulfide discharge products. To address these problems, sulfurized polyacrylonitrile (S-PAN) has been developed as a promising alternative. S-PAN is synthesized by using inexpensive sulfur and polyacrylonitrile through a straightforward thermal process in an inert environment. The high-temperature synthesis results in strong chemical bonding between sulfur and the carbonized polyacrylonitrile structure which eliminates the shuttle effect, enabling S-PAN electrodes to work efficiently in commercial carbonate-based electrolytes, achieving with a specific capacity over 700 mAh/g, excellent cycle life, and high coulombic efficiency. The main drawbacks of S-PAN are its low electrochemical potential and electrical conductivity. However, when the S-PAN is paired with a high-capacity anode (such as silicon/graphite) [1], the specific energy of the battery can exceed that using traditional lithium metal oxide cathodes as shown in Fig. 1, but a high loading of the S-PAN cathode is required to match the capacity of the anode. To improve the conductivity, we mixed carbon nanotubes (CNTs) with S-PAN powders and used ultrasonic dispersion and filtration to form free-standing S-PAN/CNT composite cathodes. When 10 wt% CNT was used in the S-PAN/CNT electrode, it was found that when the electrode was discharged at a 2C rate (Fig. 2(a)), 93.34%, 91.27% and 76.85% of the capacity could be obtained when the S-PAN/CNT loading was 2, 4, and 5 mg/cm2, respectively; however, when the loading was increased to 6 mg/cm2, the capacity dropped to less than 29.94%. When the CNT content increases to 20 wt%, the capacity increases to 59.88% with a loading of 6 mg/cm2 (Fig. 2(b)). From SEM images shown in Fig. 3, the electrical network conducted by CNTs and the interconnection with S-PAN particles can be clearly seen. The size and morphology of the S-PAN particles, as well as the increase in the size and morphology of the S-PAN particles and the decrease in the porosity of the electrode with increasing the lithiation degree can also be clearly observed. The electrochemical impedance spectroscopy was used to characterize S-PAN/CNT electrodes with different lithiation degrees and different CNT contents shown in Fig. 4. It was found that with the increase of CNT content, the ohmic resistance and charge transfer resistance decreased, while the resistance due to diffusion did not change; in addition, with the increase of lithiation degree, the charge transfer resistance decreased. Lithium-ion batteries (LIBs) with S-PAN/CNT cathode and silicon/graphite anode were constructed and tested. The above observations are consistent with the performance of LIBs. We will discuss the migration processes of electrons and ions in electrodes with high porosity and a composite of non-conductive and highly conductive materials, as well as the performance of S-PAN/CNT electrodes and full battery cells. Figure 1

Lithium-Ion Batteries receive growing attention because of their potentially high energy and power density, which are important requirements for automobile applications. Reports agreed that the positive electrode is hereby the performance limiting cell component. NxMyCz (nickel manganese cobalt spinel) is one of the most promising cathode materials, both due to its rather high operating voltage and to either high power or energy density [1]. Hereby, a compromise between high power (thin layers and, i.e., high porosity) and high energy density (thick layers and, i.e., low porosity) has to be reached, in particular for automotive applications. This demands for an extended understanding of the interplay between microstructure parameters and chemical stoichiometry of NMC cathodes on cell performance characteristics. In this study, two NMC - cathodes recovered from commercial high energy and high power cells are analyzed (i) by SEM and X-ray tomography and (ii) by Electrochemical Impedance spectroscopy (EIS). By evaluating the impedance spectra measured at 0 to 40°C and at SOC 0 to SOC 100 by the distribution function of relaxation times (DRT) [2], a physically motivated transition line model [3] was established. The microstructure parameters required for a quantitative analysis of the electrochemical loss processes were obtained by X-ray tomography data. Additionally, the exact composition is determined by energy dispersive X-ray spectroscopy (EDX) investigations The results confirm, that a NMC electrode custom tailored for high energy density is rather thick (70 µm) and made of large low-porous agglomerates of primary particles, as described in [4]. The significant difference between the NMC cathode of a high energy and a high power cell however is not, as expected, a significantly higher porosity, but a sophisticated combination of small carbon black particles and elongated carbon black fibers, enabling high discharge currents. The tortuosity of the electrode pores, which represent the transport pathways for the liquid electrolyte, is low for the high power cell, which raises the effective electrolyte conductivity significantly, when compared to the high energy cell [4]. Furthermore the high power cell features a special compound of two different NxMyCz active materials. By including all the results from EIS, DRT, X-ray tomography and EDX, an evaluation of the influence of composition and microstructure on performance characteristics of the NxMyCz cathodes will be presented.

The nearly unmatched conformality of Atomic Layer Deposition (ALD) renders it a powerful deposition technique for applications such as catalysis where high surface areas are critical, or for protective coatings on complex 3D surfaces such as powders or porous materials. In the last decade, ALD for energy storage has come into view. Advances in technology have pushed the requirements of energy storage devices, leading to novel lithium-ion battery (LIB) concepts such as 3D-structured electrodes, thin-film electrode and the combination of both. These concepts enable high-power and high-energy integrateable batteries, but require a conformal deposition technique for the current collectors, electrodes, solid electrolytes and interfacial coatings alike. Besides 3D structuring, materials design of the LIB electrodes is paramount to achieve higher power and higher energy densities, beyond traditional electrode materials such as LiCoO2, and LiMnO2which are limited to volumetric capacities of 550-700mAh/cm³. Traditionally, the main focus of materials development for batteries has been on crystalline compounds. However, several indications exist that higher energy and power density can be found in amorphous materials. ALD is not only excellently suited to deposit conformal films, but also able to grow high-quality amorphous films at low deposition temperatures, enabling the study of amorphous thin-film electrodes. In this work, ALD of vanadium oxides for applications as lithium-ion electrodes is envisioned. Vanadium oxides were amongst the first materials to be studied as LIB cathodes, but were never commercialised. V2O5 is a well-known LIB electrode, but the rather low volumetric energy density (when storing one lithium) or poor cyclability (when storing 2-3 lithium ions) have prevented its large-scale commercialisation in the past. Here, we demonstrate the ALD deposition of amorphous and crystalline V2O5, and two ‘flavours’ of amorphous VO2, from a single vanadium precursor (Tetrakis[ethylmethylamino] vanadium). We demonstrate the crystallisation of these films into crystalline films in the Wadsley series, and are able to unravel the influence of initial ALD process, atmosphere, temperature and substrate on the crystallization and oxidation of the VO2 films. With this in mind, we are able to obtain phase-pure crystalline vanadium oxides in the whole Wadsley series (VO2–V6O13–V4O9–V3O7–V2O5), which show very high energy densities up to more than double that of typical bulk cathodes (1380mAh/cm³ for V4O9). The amorphous initial states (amorphous VO2 and V2O5) are often not considered due to their lack of a clearly defined electrode potential. However, building on the nature of ALD to grow high-purity amorphous films, these were also investigated here. It was found that, besides also having very high capacities, their kinetics are excellent. Finally, the best candidates were examined on an ALD Pt-coated silicon micropillar array as 3D-structured thin-film electrodes. The 20x surface enhancement of the micropillar substrate enhanced the footprint capacity of the 40nm films from approximately 2-5µAh/cm² to 40-100µAh/cm², with the highest capacity for amorphous VO2(>100µAh/cm² for the 40nm film), while at the same time maintaining the excellent thin-film kinetics of the planar films, in effect simultaneously demonstrating the potential of ALD to deposit 3D thin-film electrodes as well as a tool to study amorphous and crystalline films. In conclusion, a wide range of crystalline and amorphous vanadium oxides were demonstrated from a single vanadium-precursor based ALD process. All films were examined as potential lithium-ion battery electrodes, and showed promise of very high volumetric capacities. In particular, the amorphous films and the crystalline VO2 (B) not only displayed very high capacities, but also excellent kinetics, enabling both high-energy and high-power electrodes. Figure 1

Novel Na0.5Bi0.5TiO3 based, lead-free energy storage ceramics with high power and energy density and excellent high-temperature stability

Lithium-ion capacitors (LICs) are flourishing toward high energy density and high safety, which depend significantly on the performance of the intercalation-type anodes used in LICs. However, commercially available graphite and Li4 Ti5 O12 anodes in LICs suffer from inferior electrochemical performance and safety risks due to limited rate capability, energy density, thermal decomposition, and gassing issues. Here a safer high-energy LIC based on a fast-charging ω-Li3 V2 O5 (ω-LVO) anode with a stable bulk/interface structure is reported. The electrochemical performance, thermal safety, and gassing behavior of the ω-LVO-based LIC device are investigated, followed by the exploration of the stability of the ω-LVO anode. The ω-LVO anode exhibits fast lithium-ion transport kinetics at room/elevated temperatures. Paired with an active carbon (AC) cathode, the AC||ω-LVO LIC with high energy density and long-term endurability is achieved. The accelerating rate calorimetry, in situ gas assessment, and ultrasonic scanning imaging technologies further verify the high safety of the as-fabricated LIC device. Theoretical and experimental results unveil that the high safety originates from the high structure/interface stability of the ω-LVO anode. This work provides important insights into electrochemical/thermochemical behaviors of ω-LVO-based anodes within LICs and offers new opportunities to develop safer high-energy LIC devices.

Crack-free single-crystalline Ni-rich layered NCM cathode enable superior cycling performance of lithium-ion batteries

Aqueous lithium-ion batteries with niobium tungsten oxide anodes for superior volumetric and rate capability