Improved Cycle Life Research Articles

Engineering Surface-Binder Interactions in High Energy Density Nanowire Conversion Electrodes for Improved Cycle Life without Fluorinated Additives

High capacity conversion electrode materials – like silicon and germanium – that undergo a large volume change upon lithiation and delithiation, require the formation of a robust solid-electrolyte interphase (SEI) layer, which is critically important to mitigate deleterious irreversible reactions that occur at the electrode-electrolyte interface. Over time, these irreversible reactions at the electrode surface result in capacity fade by decreasing the number of mobile lithium ions within the cell and by creating a more hindered diffusion path for lithium ions as they travel toward the electrode. To combat the recurrence of these irreversible reactions in high-capacity conversion electrode systems, the addition of electrolyte additives, such as fluoroethylene carbonate (FEC), is typically deemed necessary to promote stable cycling and improve capacity retention. The observed improvements associated with the inclusion of these virtually universally employed additives have been previously attributed to fluorinated reductive decomposition products that enable the formation of a robust SEI layer. Clearly, careful control over interfacial chemistry and surface reactions are critical for the design of robust electrochemical systems; however, the surface chemistry of the active material is typically ignored prior to electrode formulation. In most studies of high capacity conversion electrode materials, the surfaces remained unmodified, and the active material is incorporated irrespective of what uncontrolled – potentially oxidized – surfaces happen to be present in the native state. Herein, we systematically investigate the electrochemical cycling of germanium nanowire composite conversion electrodes with controlled surface chemistry, formulated with an array of polymeric binders, both in the presence and in the absence of fluorinated electrolyte additives. We observe that controlled modification of the nanowire electrode surface, when paired with certain binders, dramatically improved germanium nanowire-based electrode cycling retention and longevity. In fact, some of these pairings exhibit improved capacity retention in the absence of the fluorinated additives typically deemed necessary for stable cycling, whereas the addition of the fluorinated additive caused the cell capacity to fade more rapidly. Finally, through careful control of surface chemistry and strategic choice of binder material, we show that germanium nanowire-based conversion electrodes can maintain capacity retention in the complete absence of fluorinated additives, fluorinated electrolytes, and fluorinated binders.

Benzyl benzoate as an inhibitor of the sulfation of negative electrodes in lead-acid batteries

Abstract The lead sulfate crystals formed on the surface of the negative electrodes of lead-acid batteries during discharge gradually grow in size as a result of recrystallization processes. The big PbSO4 crystals have low solubility and are involved but very slightly in the charge process, thus causing progressive sulfation of the negative electrodes on cycling. In order to reduce or suppress this sulfation, the processes of PbSO4 recrystallization should be inhibited. It has been established that, besides lignosulfonates, some organic substances, too, may be used as additives to the negative active material to effectively inhibit the growth of lead sulfate crystals during battery discharge. The research results discussed in the present paper indicate that the aromatic ester compound of carboxylic acid, Benzyl benzoate (C6H5CH2O2CC6H5), has such inhibiting properties. Lead-acid test cells with negative plates containing Benzyl benzoate (BB) have improved cycle life performance, the beneficial effect of the BB additive to NAM being most pronounced at a loading level of 0.3%. Cells with BB added to the electrolyte have also been tested. In this case, the additive exhibits its inhibiting effect on the processes of PbSO4 crystal growth most strongly when added to the electrolyte at concentration levels of 0.3% or 0.5%.

Advanced Characterization Techniques in Promoting Mechanism Understanding for Lithium–Sulfur Batteries

AbstractDue to their numerous advantages, such as high specific capacity, lithium–sulfur batteries (Li–S batteries) have attracted much attention as next‐generation energy storage systems. To meet future needs for commercial application, Li–S batteries will require both improved cycle life and high energy density. It is of critical importance to understand the fundamental mechanisms in Li–S systems to further improve the overall battery performance. Various advanced characterization techniques, over the past few years, have proven their important role in promoting the mechanism understanding for Li–S batteries. Here, the recent progress of mechanism understanding, including redox reactions, Li polysulfides dissolution, etc., in Li–S systems based on the advanced characterization techniques is reviewed. Special focus is placed on how these advanced characterization techniques are being employed and what characteristic or capability they possess. The importance of the combination of multiple characterization techniques, differences between ex situ and in situ experimental methods, as well as effects of characterization conditions in Li–S batteries are also discussed.

Understanding the Improved Kinetics and Cyclability of a Li2MnSiO4 Cathode with Calcium Substitution.

Limited practical capacity and poor cyclability caused by sluggish kinetics and structural instability are essential aspects that constrain the potential application of Li2MnSiO4 cathode materials. Herein, Li2Mn1- xCa xSiO4/C nanoplates are synthesized using a diethylene-glycol-assisted solvothermal method, targeting to circumvent its drawbacks. Compared with the pristine material, the Ca-substituted material exhibits enhanced electrochemical kinetics and improved cycle life performance. In combination with experimental studies and first-principles calculations, we reveal that Ca incorporation enhances electronic conductivity and the Li-ion diffusion coefficient of the Ca-substituted material, and it improves the structural stability by reducing the lattice distortion. It also shrinks the crystal size and alleviates structure collapse to enhance cycling performance. It is demonstrated that Ca can alleviate the two detrimental factors and shed lights on the further searching for suitable dopants.

2D MoS2 as an efficient protective layer for lithium metal anodes in high-performance Li-S batteries.

Among the candidates to replace Li-ion batteries, Li-S cells are an attractive option as their energy density is about five times higher (~2,600 Wh kg-1). The success of Li-S cells depends in large part on the utilization of metallic Li as anode material. Metallic lithium, however, is prone to grow parasitic dendrites and is highly reactive to several electrolytes; moreover, Li-S cells with metallic Li are also susceptible to polysulfides dissolution. Here, we show that ~10-nm-thick two-dimensional (2D) MoS2 can act as a protective layer for Li-metal anodes, greatly improving the performances of Li-S batteries. In particular, we observe stable Li electrodeposition and the suppression of dendrite nucleation sites. The deposition and dissolution process of a symmetric MoS2-coated Li-metal cell operates at a current density of 10 mA cm-2 with low voltage hysteresis and a threefold improvement in cycle life compared with using bare Li-metal. In a Li-S full-cell configuration, using the MoS2-coated Li as anode and a 3D carbon nanotube-sulfur cathode, we obtain a specific energy density of ~589 Wh kg-1 and a Coulombic efficiency of ~98% for over 1,200 cycles at 0.5 C. Our approach could lead to the realization of high energy density and safe Li-metal-based batteries.

A dual membrane composed of composite polymer membrane and glass fiber membrane for rechargeable lithium-oxygen batteries

Development of the lithium ion-conducting membrane with high ionic conductivity and good interfacial stability is a major challenge for lithium-oxygen batteries with high energy density. Herein, we design the dual membrane composed of Li+ ion-conducting ceramic-based composite polymer membrane and glass fiber membrane. The optimized membrane exhibited a high ionic conductivity of 8.1 × 10−4Scm−1 at ambient temperature and retained an electrolyte solution well in the membrane. The dual membrane also effectively suppressed the lithium dendrite growth and blocked superoxide anion radical attack toward polymer in the composite polymer membrane. The lithium-oxygen cell employing dual membrane exhibited improved cycle life (> 70 cycles) at a constant current density of 0.1mAcm−2, which was much better than the cell with either a composite polymer membrane alone or a glass fiber membrane alone.

Prospective improvements in cost and cycle life of off-grid lithium-ion battery packs: An analysis informed by expert elicitations

This paper presents probabilistic estimates of the 2020 and 2030 cost and cycle life of lithium-ion battery (LiB) packs for off-grid stationary electricity storage made by leading battery experts from academia and industry, and insights on the role of public research and development (R&D) funding and other drivers in determining these. By 2020, experts expect developments to arise chiefly through engineering, manufacturing and incremental chemistry changes, and expect additional R&D funding to have little impact on cost. By 2030, experts indicate that more fundamental chemistry changes are possible, particularly under higher R&D funding scenarios, but are not inevitable. Experts suggest that significant improvements in cycle life (eg. doubling or greater) are more achievable than in cost, particularly by 2020, and that R&D could play a greater role in driving these. Experts expressed some concern, but had relatively little knowledge, of the environmental impact of LiBs. Analysis is conducted of the implications of prospective LiB improvements for the competitiveness of solar photovoltaic + LiB systems for off-grid electrification.

Design of Porous Solid Electrolytes for Rechargeable Metal Batteries

Recently there has been interest in porous lithium metal electrodes, which have demonstrated improvements in cycle life and charge-rate capability compared to planar lithium metal for rechargeable batteries. Here, the porous electrode consists of a rigid porous solid electrolyte with void space in the discharged state. During charge, metal plates onto the surface of the solid electrolyte, filling the pores. The rigid electrolyte's shape remains fixed. Here, we present an electrochemical model for a cell with a porous anolyte based on porous-electrode theory, and apply the model to optimize the design of the porous anolyte for energy density and mitigation of dendrites. For example, because the electronic conductivity of lithium metal is over 7 orders of magnitude higher than the ionic conductivity of present state-of-the-art solid electrolytes, electronically conductive agents are not necessary. Furthermore, if the charge-transfer resistance of the porous electrode is too low, the reaction rate can be very high next to the separator, which can have deleterious consequences for cycle life and safety. We evaluate design options for avoiding the build up of stress next to the separator.

Zipping assembly of an Fe3O4/carbon nanosheet composite as a high-performance supercapacitor electrode material.

Reasonable structure design and component selection are crucial to electrochemical performance of supercapacitor electrode materials. Sodium alginate (SA), with a novel structure which can immobilize multivalent metal cations, was used to coordinate with Fe3+ to fabricate a carbon and Fe3O4 composite by an easy sol–gel method. Due to the chelation effect between SA and Fe3+, the carbon composite was constructed into a two-dimensional sheet-like structure, and the Fe3O4 particles were nanosize and homogenously distributed on the surface of the carbon nanosheet. As an electrode material for supercapacitors, the composite electrode showed a high specific capacitance of 550 F g−1 at 1 A g−1 in the potential range from −1.1 to 0 V, and excellent cycling stability of 89% retention after 2000 cycles. The enhanced electrochemical performance could be attributed to the abundant exposed active sites, producing high pseudocapacitance, to the two-dimensional nanosheet structure, facilitating electrolyte transport and to the strong attachment strength, improving cycle life. This environmentally-friendly design can provide an alternative to existing methods, resulting in the development of a two-dimensional carbon/metal oxide composite for energy storage devices.

Enhanced Iron Molten Air Battery Cycle Life and the Chemistry of the Nickel Oxide/Air Interface

Iron molten air batteries are a promising technology for clean and efficient electrical power generation, but their durability is a key challenge to commercialization. Here, we replaced LiCl in the KCl-LiCl-LiOH system with Li2SO4 or Li0.87Na0.63K0.50CO3 to investigate electrode corrosion and improve cycle life. The nickel air electrode exhibited low corrosion rate in KCl-Li2SO4-LiOH, but the kinetics of the air electrode reactions was impaired. Electrolyte composition influences pitting corrosion of the Ni air electrode in KCl-LiCl-LiOH and intercrystalline corrosion in KCl-Li2SO4-LiOH. KCl-LiNaKCO3-LiOH is a superior electrolyte for these iron air batteries with nickel air electrode. A tenacious, compact Li nickel oxide nano-scale particle layer on the nickel air surface in KCl-LiNaKCO3-LiOH retards nickel fin matrix (current collector) corrosion allowing long-term use. The air electrode surface is an electrocatalytic layer of uniform nano-particles. The iron molten air battery cycled for 850 cycles with an average coulombic efficiency of 88.6% and average discharge potential of ∼1.04 V, achieving a ten-fold increase in cycle life in contrast with the previous result using KCl-LiCl-LiOH. This study explores key factors improving the Ni air electrode and cycle life without interfering with the cycling performance of the iron molten air battery.

Rational Evaluation and Cycle Life Improvement of Quinone-Based Aqueous Flow Batteries Guided by In-Line Optical Spectrophotometry

We measure electrolyte concentration and state-of-charge in real time in an operating aqueous anthraquinone-based flow battery using in-line optical spectrophotometry. By capitalizing on the linear transition in absorption spectra between oxidized and reduced states, we show how discontinuous capacity fade rates in redox flow batteries can be caused by a transition from one capacity-limiting electrolyte to the other, which is caused by reactant crossover. With this insight, we demonstrate an electrolyte-balancing scheme, which can be broadly applicable to flow battery systems with asymmetric electrolyte crossover rates.

Na2EDTA chelating agent as an electrolyte additive for high performance lead-acid batteries

Addition of 0.5 wt % ethylene diamine tetraacetic acid based sodium salt (Na2EDTA) chelating agent to lead-acid battery (LAB) electrolyte improves the conductance, reduces significantly the battery formation time from 3 cycles to 1 cycle due to decrease in hard sulfation, increases C rate performances (>20% increase in capacity at > 3C rates), and cycling efficiency of the battery. We present here the electrochemical performance of the conventional and corresponding Na2EDTA additive lead-acid cells by galvanostatic charge-discharge cycling, I-V characteristics, cyclic voltammetry and surface chemical aspects by using electrochemical impedance, X-ray diffraction, and scanning electron microscopy. The results indicate that the morphology of PbSO4 layer and particle size changes from spherical to rod like morphology under the influence of Na2EDTA chelating agent. In overall, addition of Na2EDTA chelating agent enhances charge acceptance, 10–20% improvement in discharge capacity and cycle life of the lead acid batteries. The superior electrochemical performance is owing to the dissociation of PbSO4 in the presence of Na2EDTA chelating agent.

Guided Lithium Metal Deposition and Improved Lithium Coulombic Efficiency through Synergistic Effects of LiAsF6 and Cyclic Carbonate Additives

Spatial and morphology control over lithium (Li) metal nucleation and growth, as well as improving Li Coulombic efficiency (CE), are among the most challenging issues for rechargeable Li metal batteries. Here, we report that LiAsF6 and cyclic carbonate additives such as vinylene carbonate (VC) or fluoroethylene carbonate (FEC) can work synergistically to address these challenges. It is revealed that LiAsF6 can be reduced to LixAs alloy and LiF, which act as nanosized seeds for Li growth and form a robust solid electrolyte interface layer. The addition of VC or FEC not only enables the uniform distribution of LixAs seeds but also improves the flexibility of the solid electrolyte interface layer. As a result, highly compact, uniform, and dendrite-free Li film with vertically aligned column structure can be obtained with increased Li CE, and the Li metal batteries using the electrolyte with both LiAsF6 and cyclic carbonate additives can have improved cycle life.

Graphene balls for lithium rechargeable batteries with fast charging and high volumetric energy densities

Improving one property without sacrificing others is challenging for lithium-ion batteries due to the trade-off nature among key parameters. Here we report a chemical vapor deposition process to grow a graphene–silica assembly, called a graphene ball. Its hierarchical three-dimensional structure with the silicon oxide nanoparticle center allows even 1 wt% graphene ball to be uniformly coated onto a nickel-rich layered cathode via scalable Nobilta milling. The graphene-ball coating improves cycle life and fast charging capability by suppressing detrimental side reactions and providing efficient conductive pathways. The graphene ball itself also serves as an anode material with a high specific capacity of 716.2 mAh g−1. A full-cell incorporating graphene balls increases the volumetric energy density by 27.6% compared to a control cell without graphene balls, showing the possibility of achieving 800 Wh L−1 in a commercial cell setting, along with a high cyclability of 78.6% capacity retention after 500 cycles at 5C and 60 °C.

Design of Porous Anolytes for Rechargeable Metal Batteries

Recently there has been great interest in porous lithium metal electrodes for rechargeable batteries, which have demonstrated remarkable improvements in cycle life and charge-rate capability compared to planar lithium metal [1]. In this type of cell design, the porous electrode consists of a porous solid electrolyte with void space in the discharged state. During charge, the metal plates onto the surface of the solid electrolyte, filling the pores. During discharge, the pores empty as lithium reacts at the surface of the electrolyte to produce lithium ions which travel through the porous electrolyte. The electrolyte is rigid, so its shape remains fixed over the life of the cell. This design is advantageous because the solid-electrolyte interphase (SEI) is stationary on the surface of the electrolyte, and therefore there is little capacity fade over cycling, because there is no volume change to cause cracks in the SEI. The design also allows space for the metal to deposit into, thereby reducing the cyclic stress of depositing metal pushing against the separator. By reducing the stress of the lithium pushing against the separator, the risk of a dendrite growing through a defect in the separator is reduced. Here we present an electrochemical model for a cell with a porous anolyte based on porous-electrode theory [2], and apply the model to optimize the design of the porous anolyte to maximize cycle life and safety. For example, we find that, because the electronic conductivity of lithium metal is over 7 orders of magnitude higher than the ionic conductivity of present state-of-the-art solid electrolytes, electronically conductive additives provide no benefit for the porous electrode. As the lithium plates onto the electrolyte surface (initially at the interface with the current collector), the plated lithium itself provides a sufficiently electronically conductive network. Furthermore, if the area-specific resistance of the porous electrode is too low, the current distribution can be highly nonuniform, which can have deleterious consequences for cycle life and safety. Finally, we discuss the implications of the model for the necessary mechanical properties of the solid electrolyte to prevent dendrites even in the presence of manufacturing tolerances.

(Invited) Enabling New Domains of Energy Storage through Atomic Layer Deposition

The portfolio of materials accessible by atomic layer deposition (ALD) processes has encompassed all key components of electrochemical energy storage (EES) – cathodes, anodes, solid electrolytes, and interphases. This provides a rich environment in which to advance the science of EES, particularly due to the exceptional thickness and conformality control inherent in underlying ALD mechanisms. Here we highlight three regimes where ALD is most promising to impact battery technology. (1) ALD-based electrode protection layers seem to offer the shortest term technology impact, providing ion permeability while serving as passivation against the varied modes chemical, electrochemical, and mechanical degradation regularly found in batteries, improving cycle life and suppressing dendrite formation. (2) ALD-based solid state batteries offer benefits in structural simplicity and control well beyond that available in commercial devices employing sputtered films. ALD solid electrolytes play a critical role in both protection layers and solid state batteries. (3) 3D solid state batteries exploit high surface areas and thin conformal layers over high aspect ratio topography to achieve higher power-energy performance than planar counterparts. Examples illustrating these opportunities include ALD LiPON protection of metal anodes and conversion electrodes, new pathways to solid electrolyte synthesis, and planar and 3D solid state batteries employing ALD for most or all components. Supported as part of the Energy Frontier Research Center (EFRC) Nanostructures for Electrical Energy Storage (NEES), funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under award number DESC0001160.

Direct Ethanol Fuel Cell for Portable Power

Introduction Portable Non-Destructive Inspection (NDI) equipment, such as Eddy Current (EC) and Ultrasonic Testing (UT), provide important tools for the Air Force to characterize flaws, cracks, and/or defects in aircraft, thus monitoring potential safety issues. Most NDI equipment is powered by a battery (alkaline, NiCad, NiMH, or Li-ion) that typically comprises a large percentage of the size and weight of the equipment. The Air Force is interested in finding alternative forms of energy for NDI equipment, due to issues with existing battery technologies that include logistical challenges, battery reliability/degradation, limited portability, and safety. Direct Ethanol Fuel Cell (DEFC) systems could potentially provide a significant advantage over conventional battery technologies, including nearly instantaneous recharging, lighter weight, longer operational times, higher power, and improved cycle life. Further, the 25-Watt power requirements of the NDI equipment are similar to a number of other portable electronics that could benefit from the technology. Materials and Methods Single cell direct ethanol fuel cells were prepared using both commercially available anion exchange membranes and experimental reduced crossover membranes. The cell anode was prepared by depositing a hydrothermally synthesized Pd-based catalyst onto a conductive carbon backing. The cell cathode consisted of pH Matter’s non-metal based oxygen reduction reaction catalyst (COR). The COR catalyst was treated with a PTFE additive to reduce ethanol crossover. The catalyst was deposited onto a commercial carbon paper (Toray) and annealed in air. Testing was completed in a nickel metal set-up with PTFE seals and consisted of mechanical compression of each component to form the cell assembly. The anode was supplied with a fuel composition consisting of 5M KOH and 5M ethanol in distilled water. Air was supplied to the cathode at approximately 25 sccm/cm2 and at ambient pressure. Cell temperature was controlled between ambient and 60°C as to prevent degradation of the cell membrane. Cyclic voltammetry curves were obtained using a PAR Versastat 3 potentiostat between OCV and 100 mV. Simulated load testing was carried out by operating the cell at a steady state current of 65 mA/cm2. Significance Fuel cells provide electricity through an efficient, pollution free, and quiet electrochemical process. However, the adoption of commercial fuel cell systems has been hampered by the logistics of providing a reliable, high purity, and low cost hydrogen [1]. Some fuel cell systems, such as SOFC and Direct Methanol, offer an opportunity to use more readily available fuels, such as liquid methanol or methane. However, these systems have been unable to achieve wide-scale commercialization due to technological challenges, such as stability and lifecycle performance.[2-3] Furthermore, methanol is considered toxic and poses environmental disposal challenges [4]. In contrast, ethanol is readily available in most markets, is liquid at room temperature, has very low toxicity, and can be readily disposed upon dilution with water. Furthermore, logistics of alcohol transport are minimal, a critical requirement for adoption in the Air Force application. In this effort, direct ethanol fuel cells were demonstrated to achieve transient power densities of 80 mW/cm2 at an operational temperature of 60°C and steady state power in excess of 20 mW/cm2, the target power required for use in NDI equipment, for greater than 20 hours. Furthermore, the replacement of fuel allowed for performance recovery of the fuel cell and continued operation in excess of 100 hours. Finally, the cells were incorporated into a full-scale stack and demonstrated under NDI operating conditions. In future work, the stack will be demonstrated with a 25-Watt prototype power system. References C. Huang, et al, Journal of Power Sources 303 (2016) 267-277T. Skalar, et al, Journal of Thermal Analysis and Calorimetry (2017) 127:265–271C. Xu, et al, Journal of Power Sources 168 (2007) 143–153Y.S. Li, et al, Journal of Power Sources 187 (2009) 387–392 Figure 1

MXenes As Candidate Cathodes for Non-Aqueous Lithium-Oxygen Batteries

Nonaqueous lithium-oxygen (Li-O2) batteries have emerged as possible high energy density alternatives to Li-ion batteries that could address the limited driving range issues faced by electric vehicles. This battery chemistry allows for high energy densities and an exceptionally high theoretical efficiency. Carbon, the current cathode catalyst, exhibits low stability against oxidation and reacts with the products formed during the discharging phase of the battery. In addition, due to other undesired side-reactions while charging the battery, all the reactants are not recovered leading to a poor rechargeability of a few cycles. A good cathode that can mitigate these issues requires careful screening and can help improve cycle life, increase capacity and help mitigate electrolyte decomposition. In this work, we focus on identifying possible cathodes from a family of intriguing two-dimensional (2D) materials known as MXenes, for lithium-oxygen batteries. MXenes have a general formula of Mn+1Xn, where M is an early transition metal and X is nitrogen or carbon, and being 2D layered materials, they have a large surface area [1]. MXenes are possible cathode candidates for lithium-air batteries owing to two considerations: (i) high electronic conductivity and (ii) high stability. We explore MXene carbides and nitrides of various transition metals as potential cathodes with low nucleation overpotentials. We use density functional theory (DFT) calculations to investigate the stability and activity of various terminated and non-terminated nitride and carbide MXenes of transition metals. We begin by exploring the MXenes of titanium and scandium such as Ti4N3, Ti4C3, Sc4N3, Sc4C3and their variants with the F, O and OH terminated groups. We observe that the nitrides are more stable than the carbides, and this trend holds also for the terminated compounds. Between the scandium and titanium MXenes, the titanium carbides are more stable than their scandium carbide equivalents; however, this observed trend is reversed for the nitride MXenes, with the scandium nitrides being more stable than titanium nitrides. The nucleation overpotential for Li-O2 batteries is determined by the adsorption free energy of the intermediate LiO2 [3]. We identify active MXene catalysts by computing the adsorption free energy through DFT calculations and we find that the non-terminated carbides and nitrides are stronger binding than the optimal binding strength. The transition metal and the termination group in the MXene are two tuning variables to weaken the binding in order achieve optimal binding strength. We will report on the activity and coverage effects of various transition metal carbide and nitride MXenes to identify promising cathodes for the Li-O2batteries.

Increasing Electrode Utilization and Developing a Robust Charging Method for Silver-Zinc Rechargeable Button Cell Batteries

Recently, silver-zinc (AgZn) rechargeable batteries have become commercially available in small sizes which have greater capacity and energy densities over comparatively sized rechargeable Li-ion and Li-polymer batteries. Silver-zinc batteries typically do not utilize 100% of their stored capacity; therefore, an accurate charging procedure needs to be employed to prevent overcharging and undercharging events. Charging the cell properly will increase the performance and cycle life. However, charging a cell without a battery management system is a considerable challenge since it is normally required to determine the state of charge of the battery accurately. This work provides a new robust charge algorithm which utilizes a two-zone charging approach. Silver-zinc rechargeable batteries have two voltage plateaus during discharge (Figure 1). Zone 1 is utilized when the cell is discharging in the lower plateau prior to charge (OCV~1.59V). Zone 2 is utilized when the cell was discharging in the upper plateau or transition zone prior to charge (OCV~1.82V). The cell is charged using a CC-CV (constant current-constant voltage) algorithm with a maximum charge current and a maximum charge voltage. Also, the use of additives in different electrolytes was explored and characterized with respect to increasing electrode utilization, charge rate capability, and cycle life improvement in silver-zinc rechargeable button cell batteries. Figure 1: Discharge voltage profile for Silver-Zinc button cell batteries Figure 1

ALD-Coated Graphite Anode Materials for Improved Cycle Life, Calendar Life, and Safety of Li-Ion Cells

Lithium-ion battery-based energy storage is widely regarded as the best technology to realize affordable electrification of automobiles (hybrids and EVs), buses, and ships. However strategies to realize higher energy density and lower cost come at the expense of cell lifetime and safety. Extensive effort has been devoted to studying the effects of ALD coatings on cathode materials, with varying reports of the impact on cycle life of full cells. However, ALD coatings on graphite anode materials have received relatively little attention, despite the role of the negative electrode in predominant energy loss mechanisms in graphite-based full cells. In this work we studied the effects of ALD coatings of Al2O3 and other chemistries on graphite active material powders, in full 95mm x 64mm pouch cells considering cycle life, calendar life, and thermal stability via ARC. We further studied the effects of different voltage windows including “high voltage” 4.4V charge limit. We found that the chemistry of the negative electrode was fundamentally altered, including SEI chemistry, growth, and resistance; and capacity slippage electrode misalignment. FTIR spectroscopy and depth-profiling XPS confirmed changes in graphite surface and SEI chemistry with ALD coatings. The result in full cells was a more stable SEI that gave significantly longer cell lifetimes and enhanced safety under conditions of high-temperature cycling, high-temperature storage, and high-voltage cycling. Moreover, we found the effects of ALD coatings on cathodes were enhanced in “Dual ALD” cells combining ALD-coated cathode materials and ALD-coated anode materials.