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Electrochemical conversion reaction based electrodes offer a high sodium storage capacity in rechargeable batteries by utilizing the variable valence states of transition metals. Thus, transition metal chalcogenides (TMCs) as such materials have been intensively investigated in recent years to explore the possibilities of practical application in rechargeable sodium-ion batteries; however, it is hindered by poor rate performance and a high-cost preparation method. In addition, some issues in regards to conversion reactions remain poorly understood, including incomplete reversible reaction processes, polarization, and hysteresis. Herein, a novel cagelike CoSe2@N-doped carbon aerogels hybrid composite was designed and prepared by a facile and high-efficiency sol-gel technology. Benefiting from the surface engineering optimization, high charge transfer, and low-energy diffusion barrier, the CoSe2@N-doped carbon aerogels exhibit a high pseudocapacitive property. Most importantly, the CoSe2 anode has been carefully investigated at different discharge/charge states by X-ray absorption near edge spectroscopy technologies and density functional theory (DFT) simulations, which deeply reveal the capacity fading mechanism and phase transition behavior.

Lithium-sulfur batteries have been considered as one of the most promising energy storage devices due to their high theoretical capacity and low cost. They go through complicated multistep electrochemical reactions from solid (sulfur)-liquid (soluble polysulfide) to liquid (soluble polysulfide)-solid (Li2S) during the discharge process. Actually, during this process, the transition from liquid phase (Li2S4) to solid phase (Li2S) at 2.1 V plateau is a difficult step with sluggish kinetics, thus leading to low sulfur utilization and discharge capacity. To promote the transition processes and enhance the sulfur utilization, CoS2@multichannel carbon nanofiber composites (CoS2@MCNFs) serving as sulfur host were successfully synthesized. Herein, CoS2 catalysts are proven to be beneficial not only for enhancing the phase-transition kinetics but also for adsorbing soluble polysulfide. Besides, unlike other carbon materials, MCNFs have plenty of hollow channels and thus enhance sulfur loading and conductivity. Accordingly, the discharge capacity increases 32% more than that of electrode without CoS2. And a very low capacity fade rate of 0.03% per cycle (over 450 cycles) is obtained at a 0.5C rate. This work has opened up new ideas for enhancing sulfur utilization for high sulfur-loading electrode.

Lithium-excess cation-disordered rocksalt oxides (DRXs) are a new class of high energy Li-ion cathode materials. A DRX cathode can deliver an exceptionally high capacity of >250 mA h g–1, implying ...

LiNi0.5Mn1.5O4 cathode material, which has a higher working voltage (4.7 v) than NCM and a moderate specific capacity (148 mAh/g theoretical), has been studied to understand the source of capacity fade during the first 100 cycles in a half cell. The work mainly consisted of high resolution TEM observations and analysis of the surface microstructural properties, before and after cycling. We found that the pristine material consisted almost entirely of large FCC spinal domains but with cycling appears small simple cubic spinel domains at the surface. It is proposed that these small changes of the surface microstructure leads to impedance rise that results in the premature arrival to the upper cutoff voltage of 4.85V during charging and the subsequent loss of capacity with cycling.

Abstract：Fracture in silicon anodes is a commonly fundamental problem, which results in ca. 80% capacity loss over the electrochemical cycles. Alginate, as one of many water-soluble polysaccharides, are efficient binder systems for silicon (Si) electrode due to their strong interface bonding with Si surface. However, the rigidness and brittleness of the polysaccharides induce dense fracture on the Si anode. In this work, a facile and effective physical approach is proposed by introducing glycerol as the plasticizer in the electrode processing. Glycerol contributes to an improvement of the ductility and flexibility of the binder, which effectively alleviates the fracture formation and propagation during repeated electrochemical cycles. At the optimum alginate/glycerol weight ratio of 2:1, silicon anode displays much improved electrochemical performances in terms of the long-term cycling performance and the rate capability. The well-preserved physical integrity of the Si anode after long-term cycles explains the electrochemical enhancement. The facile and effective dispersant optimization in electrode processing provides a new avenue for Si electrode fabrication with high electrochemical performances.

In this paper, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) is adopted as a bifunctional electrolyte additive, which is identified to effectively stabilize the surface for both gr...

Solid electrolyte interphase (SEI) has been extensively investigated in advanced lithium ion batteries, especially on graphite anode surface. However, the role of the carbon bond types on the formation of solid electrolyte interphase (SEI) on graphite surface has never been compared. In this work, single, double and triple carbon bonds on a graphite anode acting as SEI templates are comparatively investigated. Sodium propionate, sodium acrylate and sodium propynate are uniformly applied onto a natural graphite surface. It is found that different carbon types exhibit remarkable difference in the electrochemical behavior of the graphite anode. The acrylate SEI template demonstrates the best film-forming properties via in-situ polymerization between the carbon double bonds producing robust SEI film and the decorated graphite anode shows much enhanced rate capability and cycling stability. Moreover, life-span of the full cell with LiFePO4 cathode is significantly prolonged. By contrast, single and triple carbon bonds shows some limitations in the SEI formation. Therefore, constructing SEI film by in-situ polymerization of carbon double bonds is an effective strategy enhancing the durability and reliability of graphite anode.

Accelerated degradation tests can be used as the basis for predicting the performance or state of health of products and materials at use conditions over time. Measurements acquired at accelerated levels of stress are used to develop models that relate to the degradation of one or more performance measures. Frequently, products/materials of interest are subjected to variable stress levels during their lifetimes. However, testing is usually performed only at a few fixed stress levels. In such cases, cumulative degradation models are developed and assessed by using data acquired under those fixed stress conditions. The degradation rate at any stress condition within the range of the model can be estimated by the derivative of the cumulative model at that stress condition. It follows that, to predict cumulative degradation over variable use conditions, one might integrate the fluctuating degradation rate over time. Existing approaches for doing this consider degradation rates that depend only on the current stress level. Here, we propose to allow the degradation rate to also depend on the current state of health as indicated by the associated performance measure(s). The resulting modeling approach is capable of portraying a broader range of degradation behavior than existing approaches. The assertion of memoryless degradation by using this or any other approach should be assessed experimentally with data acquired under variable stress in order to increase confidence that the integrated rate model is accurate. In this article, we demonstrate the additional capability of the proposed approach by developing empirical memoryless rate-based degradation models to predict resistance increase and capacity decrease in lithium-ion cells that are being evaluated for use in electric vehicles. We then assess the plausibility of these models.

In order to combat climate change by switching from fossil fuels to renewable sources of energy generation, there is a critical need for the development of new energy storage technologies. A robust network of energy storage facilities is essential for the stability of a grid powered primarily by wind and solar. Given the scale of the need for energy storage, it is necessary for the storage technology to be low-cost, safe, and recyclable at the end of its life. At Lawrence Berkeley National Lab, we have developed a technology capable of achieving these goals. Our system is a novel flow-battery that uses a combination of strategies to address each of the above criteria. We use an aqueous (non-flammable) electrolyte and earth-abundant materials to keep projected chemical, manufacturing, and operation costs relatively low and to reduce safety concerns. Our newly developed flow-through electrode design further reduces projected manufacturing and operation costs and simplifies material recovery/recycling. Based on our prototype, the chemical cost of storage is projected to be $59/kWh compared with $66/kWh and $154/kWh for lithium ion and vanadium redox flow batteries respectively. As energy storage facilities become larger and larger, these savings from low up-front costs and efficient recycling will become increasingly important for keeping the cost of renewable energy storage affordable.