Achievable Energy Density Research Articles

The Interfacial Electronic Engineering in Binary Sulfiphilic Cobalt Boride Heterostructure Nanosheets for Upgrading Energy Density and Longevity of Lithium-Sulfur Batteries.

High gravimetric, areal and volumetric capacities together with long lifetime are key indexes for the applications of lithium-sulfur (Li-S) batteries in compact space. The sulfur host materials play pivotal roles in the practical deployment. Herein, one type of new heterostructure nanosheets composed of cobalt boride (CoB) on nitrogen, boron-codoped porous carbon (NBC), which is constructed through molten salt-assisted strategy using ZIF-67-encapsulated ZIF-8 as precursors is reported on. Benefiting from strong interfacial electronic interactions between binary sulfiphilic CoB and porous NBC, the CoB/NBC-S electrode exhibits the excellent cycling stability with low average capacity decay of 0.013% in ultralong 1500 cycles at high rate of 5 C. Remarkably, the electrode with high sulfur content of 82 wt% and high sulfur loading of 5.8mg cm-2 delivers gravimetric capacity of 1309mA h g-1 , areal capacity of 7.59mA h cm-2 , and volumetric capacity of 1355mA h cm-3 at 0.1 C. The favorable electrochemical performance can rival with the state-of-the-art of those in the reported nanosheets-based sulfur cathodes. This study provides new methodology for the design of heterostructure nanosheets of metal borides to achieve energy density and longevity of Li-S batteries.

Effects of Oxygen Cathode Substrates with Various Carbon Catalysts on the Discharge Capacity of Lithium-Oxygen Battery

Lithium-oxygen batteries have been considered strong candidates to supersede current rechargeable batteries especially lithium-ion batteries. Despite having tremendously high theoretical energy density, the practically achievable energy density is far from commercial application till date. The oxygen electrode is one of the major bottlenecks in maximizing the battery capacity. It is comprised of a porous structure (mainly carbon) with high surface area and sufficient reaction sites. High porosity facilitates lithium ion and oxygen mass transfer and results in high storage capacity for the insoluble discharge product during discharging. The cathode electrode is fabricated by coating a catalyst layer on a porous carbon substrate. The substrate, which contacts with oxygen channels, plays a vital role in mass transfer of oxygen from outside to the reaction sites. Therefore, it is important to select a substrate that does not clog with deposition of Li2O2 particles immediately after discharging begins and allows oxygen to reach the catalyst side for longer period of time.This study investigates the effects of oxygen electrode substrates with various coating materials on the discharge capacity of lithium-oxygen battery. For this purpose, we have compared the discharge capacity of plain carbon cloth, plain carbon paper and carbon cloth or carbon paper coated with carbon catalysts including Vulcan XC, Super P and Graphene Oxide. 1.5mg/cm2 (+/-0.3mg/ cm2) is used as catalyst loading. The electrolyte used in this study is 1M LiTFSI in TEGDME. PTFE (30wt%) is used as a binder. All experiments are conducted at room temperature with pure oxygen supply.With carbon cloth as a substrate, the discharge capacities obtained were 3 to 6 times higher (depending on the carbon catalysts coated) than the capacities obtained with carbon paper. The bare carbon cloth, Vulcan XC, Super P and Graphene oxide with carbon cloth as a substrate have discharge capacities of 0.11 mAh/mg, 13 mAh/mg, 6.8 mAh/mg, 1.5 mAh/mg respectively. On the other hand, the discharge capacities achieved with bare carbon paper, Vulcan XC, Super P and graphene oxide with carbon paper as substrate were 0.02 mAh/mg, 2.4 mAh/mg, 2.7 mAh/mg, 0.28 mAh/mg respectively. The results clearly indicate that the cathode with carbon cloth as a substrate yields significantly higher discharge capacity with all the coating materials as compared with the carbon paper. The different performances of two substrates can be attributed to their structure and pore size distribution. Carbon cloth is composed of flexible woven threads with longer lengths ( ̴ 30µm) and broader pore size distribution (5-200 µm) with peaks at 10, 70 and 100 µm. This type of structure is favorable in reducing tortuosity, enhancing mass transport of oxygen and lithium ion and improving ionic conductivity. On the other hand, the structure of carbon paper comprises of non-woven short carbon fibers ( ̴ 15µm) and smaller pore size distribution range (10-70 µm) with a peak at 50 µm. This renders poor transport of oxygen from outside to the reaction sites leading to lower discharge capacity.The primary function of coating materials is to increase surface area of cathode thereby providing more reaction sites and creating tri-phase boundaries for reaction to take place. These catalysts also have different pore size distributions and resistance to mass transfer. Therefore, various carbon catalysts used yield different discharge capacity with same substrate.

Analysis of Germanium Nanoparticle Composites with an Aluminum Current Collector toward Li-ion Battery Anodes with High Capacity and Broad Potential Stability Range

Reduction reactions with lithium at >0.3 V vs Li/Li+ make germanium prospectively compatible with aluminum current collectors to form a copper-free lithium-ion cell anode that may enable lithium-ion cells that are more tolerant to overdischarge. Targeted 2.0 mAh/cm2 germanium nanoparticle electrodes with an aluminum foil (Ge–Al electrode) current collector were fabricated and tested versus lithium from 0.3 to 1.5 V vs Li/Li+ in 1.0 M LiPF6 1:1 ethylene carbonate/diethyl carbonate (v/v) electrolyte and demonstrated a peak reversible capacity of 342 mAh/gGe at a targeted C/10 rate. A targeted 2.0 mAh/cm2 germanium nanoparticle electrode with a copper current collector (Ge–Cu electrode) was also tested from 0.005 to 1.5 V vs Li/Li+, the results of which are utilized as a representative comparison of germanium tested in a conventional lithium-ion anode potential range. Compared to the Ge–Cu electrode, after 50 cycles at a targeted C/10 rate the Ge–Al electrode showed 90% vs 18% capacity retention. Post-mortem analysis with XPS, SEM/EDS, Raman spectroscopy, and FTIR showed that compared to the Ge–Cu electrode the Ge–Al electrode had (1) less oxygen, fluorine, and carbon deposition, (2) less germanium amorphization, (3) formation of LixCy and Ge–H, and (4) less Li2O formation. After 150 cycles at equivalent targeted rates, the Ge–Al electrode also had significantly less mid-frequency impedance growth than the Ge–Cu electrode. Modeling of 18650 format LiNiCoAlO2-cathode lithium-ion cells with a Ge–Al anode predicted an achievable energy density and specific energy of up to 491 Wh/L and 198 Wh/kg. A germanium dissolution potential of 4.2 V vs Li/Li+ was assigned based on voltammetry and post-mortem SEM/EDS. Cycling of a Ge–Al electrode with an upper potential cutoff of 4.2 V vs Li/Li+ every tenth cycle showed 30% capacity retention after 50 cycles, an increased capacity fade attributed to solid electrolyte interphase instability up to 4.2 V vs Li/Li+ based on impedance and post-mortem analysis.

Understanding implications of cathode architecture on energy density of solid-state batteries

Next generation solid-state batteries (SSB) will need to leverage high voltage cathodes, as well as metallic anodes to achieve the realistic performance targets necessary to replace liquid electrolyte-based batteries in cutting-edge applications including electric vehicles. However, limitations arising from mass and charge transports, kinetics and chemo-mechanical degradation at the electrode | electrolyte interface limit the performance of present day SSBs. Optimizing composite cathode architecture, which is an integral part of solid-state batteries, is vital to realize the high-energy density and high-performance goals for next-generation solid-state batteries. Cathode architecture needs to be optimized for high loadings of active material, well-percolated ion and electron transport pathways and increased resilience against electrochemical stresses. This paper provides a first report of framework for geometric modeling of composite cathode architectures and evaluates the impact of cathode architecture on cell-level energy density using hierarchical models. Packing around primary and secondary active material particles are simulated for a range of active material particle size and solid electrolyte size distributions in the composite cathode. Impact of packing architecture on processing parameters of a given cathode composition and thickness, as well as on achievable energy density is evaluated for a range of commonly used solid electrolyte and cathode materials. Overall, the proposed framework offers a facile exploratory methodology for establishing initial metrics for scalable processing of practical and competent SSBs.

Impact of a Gold Nanocolloid Electrolyte on Li2O2 Morphology and Performance of a Lithium-Oxygen Battery.

Aprotic lithium-oxygen batteries currently suffer from poor cyclic stability and low achievable energy density. Herein, gold nanoparticles capped with mercaptosuccinic acid are dispersed in 1.0 M LiClO4/dimethyl sulfoxide (DMSO) as a novel electrolyte for lithium-oxygen batteries. Morphological and electrochemical analyses indicate that film-like amorphous lithium peroxide is formed using the gold nanocolloid electrolyte instead of bulk crystals in battery discharging, which apparently increases the conductivity and accelerates the decomposition kinetics of discharge products in recharging, accompanied by the release of incorporated gold nanoparticles with the decomposition of lithium peroxide into the electrolyte. Experiments and theoretical calculations further demonstrate that the suspended gold nanoparticles in the electrolyte can adsorb some intermediates generated by an oxygen reduction reaction, which effectively alleviates the cleavage of the electrolyte and impedes the corrosion of the lithium anode. As a result, the life span of lithium-oxygen batteries is dramatically increased from 55 to 438 cycles, and the rate performance and full-discharge capacity are also massively enhanced. The battery failure is attributed to the degradation of gold nanocolloid electrolytes, and further studies on improvement of colloid stability during battery cycling are underway.

Practical assessment of the performance of aluminium battery technologies

Aluminium-based battery technologies have been widely regarded as one of the most attractive options to drastically improve, and possibly replace, existing battery systems—mainly due to the possibility of achieving very high energy density with low cost. Many reports have demonstrated primary or rechargeable Al-based battery chemistries in both aqueous and non-aqueous electrolytes. However, the practical realization of these battery chemistries has been difficult over a long period of time (170 years). In fact, no Al-based battery has been shown with the required stability or touted energy density. Typically, the performance of Al-based batteries is overstated in the literature due to imprecise considerations that do not fairly evaluate practically achievable energy densities. Here we provide accurate calculations of the practically achievable cell-level capacity and energy density for Al-based cells (focusing on recent literature showing ‘high’ performance) and use the results to critically assess their future deployment. Performance breakthroughs in rechargeable batteries are regularly reported in academic publications. Here the authors closely examine literature data on aluminium batteries and offer a realistic perspective on the technology.

(General Student Poster Session Winner - 1st Place)Feasibility of LiNbO3 Surface Coating on High-Ni Layered Cathode Materials for Lithium Ion Batteries

Recently, lithium ion batteries (LIBs) have received great attention as a suitable power source for electric vehicles (EVs) because of its highest energy and power densities among currently available energy storage systems. For successful implementation the achievable energy density of current LIBs should be further improved to meet the industrial requirements. In this respect, the development of advanced materials is crucial for improving the energy density of LIBs. During the last decade, layered lithium transition metal oxides (e.g., LiMO2, M = transition metal) have been used as the most popular cathode materials in commercial LIBs [1]. From a structural point of view, Li+ can be reversibly inserted and extracted in the given structure based on the redox reactions of transition metals. Therefore, the choice of transition metals is crucial for determining the electrochemical properties of these cathode materials. By increasing the Ni concentration, the reversible capacity of the cathode materials can be effectively increased due to the double redox reaction of Ni2+/Ni4+. In practice, high-Ni layered cathode materials (Ni > 80%) can offer a high reversible capacity over 200 mAh g-1 [2]. As a result of increasing the Ni concentration, however, the cathode materials suffer from poor cycle performance and thermal stability mainly induced by side reactions with electrolyte and residual Li at the surface. To overcome these limitations, effective surface coatings are required to make the surface more stable and suppress undesirable side reactions [3]. Herein, we propose a surface coating with LiNbO3 onto NCM811 cathode material to minimize undesirable side reactions as well as improve the thermal stability [4]. Thanks to the high ionic conductivity and thermal resistance of LiNbO3, LiNbO3 coated NCM811 exhibit much improved cycle performance and rate capabilities even at high operating temperature of 60 oC. Moreover, we also investigate the effect of LiNbO3 crystallinity on the electrochemical properties of LiNbO3 coated NCM811. It would provide a practical guideline for the development of a highly reliable high-capacity cathode material for EV applications.

Evaluating the Deployment of Al Anodes in Primary and Secondary Batteries: Current Status, Future Prospects?

For decades, aluminum anodes have been looked at as the holy grail for many battery chemistry platforms, promising to increase the gravimetric and volumetric energy density to new heights while keeping battery costs low. However, its deployment has been beset with problems, the most notable of which have been corrosion and surface passivation in investigated electrolytes. Researchers have tried to work around these issues through a combination of electrolyte additives, synthesis of new material morphologies, galvanic protection, and changing the material chemistry by moving away from traditional electrolytes. Each of these approaches have had moments of promise, but they also come with their own limitations and challenges that have practical implications – including practically achievable energy density, rate capability, materials and manufacturing cost, and lifetime. Another complicating factor is that the technical literature (publications and patents) often present only an overwhelmingly sunny outlook for a given approach or technology, even when such an outlook is not reasonably supported by data. This makes it very difficult to understand which of the approaches that have been tried have the potential to be deployed in practical, commercial batteries. This presentation will systematically present and analyze the main deployments of Al anodes in both primary and secondary batteries using aqueous and non-aqueous electrolytes. The focus of this talk with be to be quantitative with regards to the practically-achievable energy density and lifetime of some of the most promising aluminum technologies from the literature and to provide a critical assessment of the state of the field today and the future for Al in primary and secondary energy storage.

(Invited) Tailored Design of Polymer Electrolytes for Advanced High-Capacity and High-Voltage Lithium Batteries

For decades, the use of polymer-based lithium battery electrolytes has been restricted to cells containing low-voltage positive electrodes such as LiFePO4, which intrinsically limited the achievable energy density. On the other hand, the employment of polymer electrolytes allowed for the use of lithium metal negative electrodes, even though the operation remained limited to elevated temperatures due to the relatively low ionic conductivity at room temperature.1,2 Accordingly, if these two challenges, i.e., the limited stability towards oxidation and the poor ionic conductivity, could be overcome, polymer-based electrolytes may pave the way towards high-energy lithium-metal batteries – one of the main targets of global battery research activities.3,4 Herein, we report our latest achievements in this field, specifically for single-ion conductors, as they additionally provide highly homogeneous lithium deposition and suppress the detrimental occurrence of reversed cell polarization upon cycling.2,5 These achievements include the design of polymer electrolytes with enhanced single-ion conductivities of about 10-3 S cm-1 at 30 °C as well as excellent stability towards lithium metal and high-energy next generation cathode materials like Li(Ni0.8Mn0.1Co0.1)O2 – up to anodic cut-off potentials as high as 4.5 V. As a result, these new single-ion conducting polymer electrolytes allow for highly stable cycling of such cells at 20 °C and even 0 °C.6,7 We hope that this work will trigger further research efforts also in other labs to boost the development of advanced lithium-polymer batteries. References J. Kalhoff, G. G. Eshetu, D. Bresser, and S. Passerini, ChemSusChem, 8, 2154–2175 (2015).D. T. Hallinan and N. P. Balsara, Annu. Rev. Mater. Res., 43, 503–525 (2013).X.-B. Cheng, R. Zhang, C.-Z. Zhao, and Q. Zhang, Chem. Rev., 117, 10403–10473 (2017).Y. Guo, H. Li, and T. Zhai, Adv. Mater., 29, 1700007 (2017).H. Zhang et al., Chem. Soc. Rev., 46, 797–815 (2017).H.-D. Nguyen et al., Energy Environ. Sci., 11, 3298–3309 (2018).Z. Chen et al., submitted manuscript.

Waterborne Nanocomposites with Enhanced Breakdown Strength for High Energy Storage

Polymers have been considered as promising materials for dielectric energy storage because of their high breakdown strength, favorable flexibility, and processability. The achievable energy density...

Recent advances in the mitigation of dendrites in lithium-metal batteries

Utilizing lithium (Li) metal as the anode can enable lithium metal battery (LMB) systems to achieve energy densities of up to 1150 Wh Kg−1, approaching that of gasoline. However, the use of Li metal is plagued with a whole host of problems, the most serious of which is the issue of nucleation of Li metal dendrites. These dendrites grow inexorably on charge–discharge cycling, piercing through the battery separator membrane and eventually electrically shorting the battery. This can result in thermal runaway leading to an unacceptable fire hazard. In this review article, we focus on recent advances in mitigating, suppressing, and healing Li metal dendrites in LMBs with liquid electrolytes. We discuss a whole host of exciting approaches including electrolyte engineering, interface engineering, the use of stable Li hosts, homogenizing Li-ion flux, and the physical healing of dendrites using temperature fields. We discuss the pros and cons of these approaches and provide our perspectives for future research directions. In particular, it is important to consider dendrite mitigation in a full-cell setting and with a realistic form factor such as prismatic or cylindrical cells. Given the multifaceted nature of the dendrite challenge, it is unlikely that there is a single magic solution, making it necessary to explore a combination of strategies to work in synergy to make Li metal anodes viable in commercial systems.

Hydrogen/Vanadium Hybrid Redox Flow Battery with enhanced electrolyte concentration

A high energy density Hydrogen/Vanadium (6 ​M HCl) system is demonstrated with increased vanadium concentration (2.5 ​M vs. 1 M), and standard cell potential (1.167 vs. 1.000 ​V) and high theoretical storage capacity (65 ​W h L−1) compared to previous vanadium systems. The system is enabled through the development and use of HER/HOR catalysts with improved chemical stability towards the halogen-containing electrolyte within which the usual catalyst (Pt/C) is shown to quickly degrade during potential hold experiments. The implementation of an Ir/C catalyst at the negative side enables a system with high achievable energy density of 45 ​W ​h ​L−1 at 75 ​mA ​cm−2 associated with 67% electrolyte utilization. Based on such a promising performance, the system here presented could be a suitable solution for medium and large-scale energy storage with lower cost and volume footprint than existing batteries, particularly all-vanadium RFBs.

Reversible Actuation via Photoisomerization-Induced Melting of a Semicrystalline Poly(Azobenzene).

Photoisomerization of azobenzene in polymer matrices is a powerful method to convert photon energy into mechanical work. While most previous studies have focused on incorporating azobenzene within amorphous or liquid crystalline materials, the limited extents of molecular ordering and correspondingly modest enthalpy changes upon switching in such systems has limited the achievable energy densities. In this work, we introduce a semicrystalline main-chain poly(azobenzene), where photoisomerization is capable of reversibly triggering melting and recrystallization under essentially isothermal conditions. These materials can be drawn into aligned fibers, yielding optically driven two-way shape memory actuators capable of reversible bending.

Study of Mn(III) Disproportionation Reaction Using Vanadium and Titanium Additives: Application to Redox Flow Batteries

Manganese, an earth-abundant transition metal, exists as Mn(III)/Mn(II) redox couple at a standard potential of +1.51V vs. SHE. It has drawn interest for implementation as positive side in V/Mn redox flow battery (RFB) due to higher achievable energy density than all-vanadium RFB. Unfortunately, Mn(III) disproportionation into Mn(II) and MnO2(s) led to loss of capacity, pressure drop increase and passivation of electrode surface during RFB cycling. We studied the influence of Ti(IV) or V(V) additives on Mn(III) stability in high acidic medium, by formulating 4 different electrolytes at equimolar ratio (Mn, Mn:Ti, Mn:V:Ti, Mn:V). Electrochemical characterizations reveals Mn(III) involvement in a complex nucleation/growth process at the electrode surface, along with its disproportionation. SEM combined to XPS demonstrates different oxide layers morphologies and chemical nature: MnO2 was formed in the presence of Mn and Mn:Ti, and MnO in the presence of V(V). Spectroelectrochemical study of Mn electrolytes highlights the displacement of the disproportionation reaction equilibrium in the presence of Ti(IV) or V(V) additives. Below 10% of electrolyzed Mn(III) was involved in the disproportionation reaction in the presence of Ti(IV) and V(V) (e.g., 25% without additives). V(V) was observed to enhance the stability of Mn(III) as compared to Ti(IV), which is of high interest for redox flow battery applications. In fact, Mn:V electrolyte could be used instead of Mn:Ti as the positive side of a Mn-V RFB will considerably reduce cross-contamination issues. As observed in the spectroelectrochemical study, the battery might be charged up to 90% SOC without loss of capacity. Moreover, in case of MnO particles formation, the strong acidic conditions will directly dissolve the particles preventing the battery from electrode passivation or/and pressure drop concerns. Figure 1

Design Principles to Govern Electrode Fabrication for the Lithium Trivanadate Cathode

A full depth of discharge mathematical model for the lithium trivanadate cathode, considering lithiation of the layered α-phase, phase change, and lithiation of the rock-salt like β-phase at lower potentials, is developed. The coupled electrode-scale and crystal-scale model is fit to electrochemical data, and additionally validated with operando EDXRD. There is good agreement between the simulated and measured spatial variation of the volume fraction of the β-phase. This mathematical model is used to guide electrode fabrication, accounting for both ionic and electronic transport effects. Values of three design parameters—electrode thickness, porosity, and volume fraction of conductor—are identified, and the sensitivity of the energy density to these design parameters is quantified. The model is also used to investigate electrode design to create electrodes that deliver the maximum achievable energy density under the constraint that the α to β-phase transition is avoided, since phase change has been demonstrated to reduce cycle life. The energy density sacrificed to avoid phase change decreases at higher discharge rates, but the target values for electrode fabrication remain the same as those when optimizing the electrode for the full depth of discharge.

Tailoring the Charge/Discharge Potentials and Electrochemical Performance of SnO2 Lithium‐Ion Anodes by Transition Metal Co‐Doping

AbstractIt has been shown that the introduction of several transition metal (TM) dopants into SnO2 lithium‐ion battery anodes can overcome the issues associated with the irreversible capacity loss from the conversion reaction of SnO2 and the aggregation of the metallic Sn particles formed upon lithiation. As the choice of the single dopant, however, plays a decisive role for the achievable energy density – precisely its redox potential – we investigate herein TM co‐doped SnO2, prepared by using a readily scalable continuous hydrothermal flow synthesis (CHFS) process, to tailor the dis‐/charge profile and by this the energy density. It is shown that the judicious choice of different elemental doping combinations in samples made via CHFS simultaneously improves the cycling performance and the full‐cell energy density. To support these findings, we realized a lithium‐ion full‐cell incorporating the best performing co‐doped SnO2 as negative electrode and high‐voltage LiNi0.5Mn1.5O4 (LNMO) as positive electrode–to the best of our knowledge, the first full‐cell based on such anode material in combination with LNMO as cathode active material.

Flexible and Adaptable Fuel Cell Pack with High Energy Density Realized by a Bifunctional Catalyst.

A proton exchange membrane fuel cell (PEMFC) system with a hydrogen generator could have higher energy density than flexible batteries and supercapacitors and is possible to meet the urgent demand of flexible electronics. However, a flexible PEMFC pack is still not available due to the absence of a flexible hydrogen generator. To solve this problem, we successfully invented a flexible and adaptable hydrogen generator, which was realized by a new bifunctional aerogel catalyst with the abilities of both storing and producing hydrogen. The flexible hydrogen generator can produce hydrogen at room temperature when the device is inverting, bending, and rotating. By combining this flexible hydrogen generator and the unique flexible PEMFC stack of our group, we originally made a highly flexible and adaptable fuel cell pack with a high theoretical energy density (up to 722 Wh·kg-1) and current achieved energy density (135.9 Wh·kg-1). Such a PEMFC pack is highly promising to meet the high demand of flexible electronics.

Electrodes with Electrodeposited Water-excluding Polymer Coating Enable High-Voltage Aqueous Supercapacitors.

Aqueous supercapacitors are powerful energy sources, but they are limited by energy density that is much lower than lithium-ion batteries. Since raising the voltage beyond the thermodynamic potential for water splitting (1.23 V) can boost the energy density, there has been much effort on water-stabilizing salvation additives such as Li2SO4 that can provide an aqueous electrolyte capable of withstanding ~1.8 V. Guided by the first-principles calculations that reveal water can promote hydrogen and oxygen evolution reactions, here, we pursue a new strategy of covering the electrode with a dense electroplated polymerized polyacrylic acid, which is an electron insulator but a proton conductor and proton reservoir. The combined effect of salvation and coating expands the electrochemical window throughout pH 3 to pH 10 to 2.4 V for both fast and slow proton-mediated redox reactions. This allows activated carbon to quadruple the energy density, a kilogram of nitrogen-doped graphene to provide 127 Watt-hour, and both to have improved endurance because of suppression of water-mediated corrosion. Therefore, aqueous supercapacitors can now achieve energy densities quite comparable to that of a lithium-ion battery, but at 100 times the charging/discharging speed and cycle durability.

Materials electrochemistry for high energy density power batteries

On June 30th of 2019, China Association for Science and Technology announced the list of twenty questions that are considered either of guiding importance for frontiers of sciences or playing crucial roles in technological and industrial innovation. Among which the question 4 is “materials electrochemistry for high energy density power batteries”. This article is an interpretation of this question, including a basic overview of the current technology, industry and market of lithium ion battery for powering electric vehicles, the trends of future development, and where the scientific problems are. Along with the rapid economic development in the last a few decades, the vehicle market in China has grown dramatically in recent years. The total number of vehicles in China is already exceeding 0.2 billion, which makes twenty percent of the total number in the world. And this number keeps increasing at a fast pace since the number of vehicle per capital in China is still much lower than those of developed countries (the average number of vehicles per thousand person at year 2016: China-140, USA-797, Japan-591, Korea-376). The huge number of vehicles in China consume a large amount of fuel oil (about 50% of the total fuel oil consumption of China every year are attributed to vehicles), which is prepared from petroleum, a scarce resource in China. Fossil fuel consumption also causes severe air pollution that threatens people’s health and results in global environmental concerns considering the consequences arising from the excessive emission of Greenhouse Gases such as CO2. Development of electric vehicles (EVs) to replace fossil fuel consuming vehicles is a promising solution to tackle the fossil energy exhaustion, global warming, and environment pollution problems, realizing a low-carbon society, and is also an opportunity for China to develop the automobile industry. However, the energy density of the current power batteries used in the EVs is still much lower than that of the fossil energy, which causes the so-called “range anxiety” in EV drivers, hindering the mass-market penetration of EVs. Therefore, overcoming the “range anxiety” by developing higher energy density power batteries is a critical technological challenge for innovative revolution of the vehicle market. Usually, driving ranges of at least 500 km are required for EVs to achieve wide customer acceptance. However, the state-of-the-art lithium-ion battery, which has the highest energy density among all mass-produced rechargeable battery systems, barely meets this requirement when battery safety and cycle lifetime are also concerned. Since the energy density of rechargeable batteries is in principle determined by the active anode and cathode materials, the development of new materials chemistry and electrochemistry is the central scientific task for the popularization of EVs. A survey of currently or potentially available active materials is thus helpful in making a technologically sound forecast of battery energy density as well as in setting up EV development roadmap. In this paper, we briefly go through the materials electrochemistry for current and future active materials for lithium ion batteries and lithium metal batteries, thus including both intercalation and conversion reaction mechanisms, and assess the potential of these active materials in the coming decade to achieve energy density as high as 300 Wh/kg or even higher. The scientific questions and technological challenges that need to be addressed to achieve the goal are analyzed and emphasized. We hope this article will help the readers to unravel the complex power battery market, and potentially inspire researchers in the field to solve the “materials electrochemistry for high energy density power batteries” problem.

Ternary nanocomposite of cobalt oxide nanograins and silver nanoparticles grown on reduced graphene oxide conducting platform for high-performance supercapattery electrode material

The ternary nanocomposite of cobalt oxide (Co3O4) and silver (Ag) nanoparticles with reduced graphene (rGO) was successfully synthesized via single-step hydrothermal method and applied as a positrode material in supercapattery. The successful synthesis of ternary nanocomposite (rGO-Co3O4–Ag) and uniform distribution of Co3O4 nanograins over graphene matrix decorated with Ag nanoparticles was confirmed using X-ray diffraction, field emission scanning electron microscope, energy-dispersive X-ray and X-ray photoelectron spectroscopy. From electrochemical studies such as cyclic voltammetry, galvanic charge-discharge and impedance spectroscopy, it was found that the prepared ternary nanocomposite exhibited excellent performance compared to its counterparts (Co3O4, rGO-Co3O4). The rGO-Co3O4–Ag ternary nanocomposite showed a specific capacity of 94.20 C g−1 that is remarkably higher than the rGO-Co3O4 (63.98 C g−1) and Co3O4 (58.92 C g−1) in a three-electrode cell system using 1 M KOH electrolyte. The two electrodes cell assembly (supercapattery) was fabricated using rGO-Co3O4–Ag nanocomposite as a positrode and activated carbon as a negatrode. The assembled supercapattery (rGO-Co3O4–Ag/activated carbon) was able to run in a potential range of 0–1.5 V even at the higher scan rate. The two electrodes cell studies demonstrated that the assembled supercapattery at a current density of 0.6 A g−1 achieved energy density and power density of 23.63 Wh kg−1 and 440 W kg−1 respectively. It also displayed excellent cycling stability with capacity retention around 85.5% after 3000 cycles at a current density of 3 A g−1.