Full Cell Cycle Research Articles

Influence of carbon coating on the electrochemical performance of SiO@C/graphite composite anode materials**Project supported by the State Grid Technology Project, China (study on the mechanism and characterization of lithium dendrite growth in lithium ion batteries, Project No. DG71-17-010), the National Key Research and Development Program of China (Grant No. 2017YFB0102004), and the National Natural Science Foundation of China (Grant No.

Silicon monoxide (SiO) has been considered as one of the most promising anode materials for next generation high-energy-density Li-ion batteries (LiBs) thanks to its high theoretical capacity. However, the poor intrinsic electronic conductivity and large volume change during lithium intercalation/de-intercalation restrict its practical applications. Fabrication of SiO/C composites is an effective way to overcome these problems. Herein, a series of micro-sized SiO@C/graphite (SiO@C/G) composite anode materials, with designed capacity of , are successfully prepared through a pitch pyrolysis reaction method. The electrochemical performance of SiO@C/G composite anodes with different carbon coating contents of 5 wt%, 10 wt%, 15 wt%, and 35 wt% is investigated. The results show that the SiO@C/G composite with 15-wt% carbon coating content exhibits the best cycle performance, with a high capacity retention of 90.7% at 25 °C and 90.1% at 45 °C after 100 cycles in full cells with LiNi0.5Co0.2Mn0.3O2 as cathodes. The scanning electron microscope (SEM) and electrochemistry impedance spectroscopy (EIS) results suggest that a moderate carbon coating layer can promote the formation of stable SEI film, which is favorable for maintaining good interfacial conductivity and thus enhancing the cycling stability of SiO electrode.

Synergetic Coupling of Lithiophilic Sites and Conductive Scaffolds for Dendrite‐Free Lithium Metal Anodes

AbstractLithium metal is highly considered as an ideal anode material because of its ultrahigh theoretical capacity of 3680 mA h g−1 and the lowest potential of −3.04 V versus the standard hydrogen electrode. However, uncontrollable lithium dendrite growth severely impedes the practical applications of lithium metal batteries. The introduction of a lithium host is an effective strategy to inhibit lithium dendrite growth, where lithiophilicity and conductivity of the lithium host play the dominant role. In this contribution, the synergistic effect of lithiophilic sites and conductive scaffolds is investigated to construct an optimized lithium host for dendrite‐free lithium metal anodes. Consequently, the lithium host with balanced lithiophilicity and conductivity demonstrates excellent electrochemical performances regarding to high Coulombic efficiency of 98% stable for 300 cycles at 1.0 mA cm−2 and improved capacity retention of 86.2% after 100 cycles in LiFePO4 full cells. The synergistic coupling of lithiophilicity and conductivity of lithium hosts enhances the understanding of lithiophilic chemistry to achieve next‐generation high‐performance batteries.

Full-Cell Cycling of a Self-Supporting Aluminum Foil Anode with a Phosphate Conversion Coating.

Aluminum foil is a promising candidate anode material for lithium-ion batteries (LIBs), due to its high theoretical capacity, low lithiation voltage, and abundance. However, as a matter of fact, it has been a great challenge to make Al foil cycle in full cells at industrially acceptable areal capacities of 2-4 mAh/cm2 for commercial 18650 LIBs and some high-power LIBs. In this study, we defined the concepts of electrochemical true contact area (ECA) (areas with perfect electrolyte/electrode contact) and electrochemical noncontact area (ENA) (referred to regions without electrolyte spread on) for the metal foil anode. An initial ECA/ENA partition would cause severe inhomogeneity of the alloying reaction, cause localized electrode pulverization, and exacerbate ECA/ENA inequality even more. Through a phosphate conversion coating on aluminum foil, we killed two birds with one stone: first, the Al foil with a phosphate conversion coating has improved wettability (characterized by the contact angle that decreased from 35.2 to 15.9°) and favors the elimination of ENA, thus guaranteeing uniform electrochemical contact; also, the coating functions as an artificial solid electrolyte interface, which stabilizes the fragile naturally formed solid electrolyte interface and a "steady-state" electrolyte/electrode interface. Therefore, when pairing the phosphated Al foil anode against a commercial LiFePO4 (LFP) cathode (with ∼2.65 mAh/cm2), it can cycle 120 times without Li excess and stabilizes at 1.27 mAh/cm2.

Boosting the cycling stability of LixSi alloy microparticles through electroless copper deposition

LixSi alloy as one of the most promising Li-containing anode candidates, but with the huge volumetric change and poor cyclability concerns, is still far away from its implementation. Nanostructuring has been proven effective to address these failure modes of Si-based anodes. However, issues of high cost and poor electrical connection of Si nanostructures are remained to be solved. Si microparticles as a low-cost alternative are feasible in practical applications. Here we report a novel LixSi/Cu alloy composites anode material synthesized through electroless copper deposition and thermal lithiation processes, using low-cost micrometer-sized Si starting materials. The sufficient Cu additives greatly enhance the electronic conductivity, and meanwhile, act as effective volumetric buffer maintaining the electrode structures during cycling. Consequently, the resultant LixSi/Cu composites (with traces of Ag, Sn, Pd) anode is able to maintain a stable structure and stable cycling in half cells (200 cycles with 74% capacity retention, ∼1100 mAh g−1 maintained). And the improved cycling stability is further demonstrated by symmetric cell tests. The anode is also paired with commercial LiFePO4 cathode to build practical battery, achieving a stable full-cell cycling (100 cycles, ∼92% capacity retention) with high Coulombic efficiency (99.5% at the third cycle and ∼99.8% for subsequent cycles).

Probing the Interactions and Dynamics in an Ionic Liquid – Organic Solvent Hybrid Electrolyte System for Potential Application in Li-S Batteries

The depletion of fossil fuel and strict environmental regulation on carbon footprints has prompted a greater reliability on sustainable energy sources. Batteries represent an important energy storage option due to their wide range of applicability and portability, however, for certain applications such as transportation, a higher energy density battery is required. Beyond the conventional Li-ion battery system, current research is focusing on next-generation cost effective devices. Amongst them, the Li-S battery technology is very promising due to its high theoretical capacity and energy density [1]. However, the chemistry involved in the Li-S battery is a complex process with multiple consecutive electrochemical reactions. Despite having many advantages, its application is still limited by several issues, e.g., the dissolution and diffusion of intermediate polysulphides, unstable plating and stripping of Li metal, both resulting in rapid capacity fading [2]. Previously, we reported the application of a novel electrolyte system composed of N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide, C3mpyrFSI, ionic liquid (IL) and 1,2 dimethoxyethane (DME) in the presence of varying saturated lithium bis(fluorosulfonyl)imide, LiFSI which predominantly suppressed the polysulphide dissolution and diffusion while showing improved lithium plating and stripping behavior [3]. In order to expand our understanding on the role of DME and the lithium salt concentration; in this work, we have considered a similar ionic liquid based electrolyte system but at a constant concentration of LiFSI salt. The ionic interactions among different species of the electrolyte system have been extensively studied by nuclear magnetic resonance (NMR) spectroscopy using 1D chemical shift, PFG-NMR and Heteronuclear Overhauser Effect SpectroscopY (HOESY) measurements. We found that, when increasing the DME concentration in the system, a strong association of Li+ cation with the DME occurs due to the electronegative oxygen atoms present in the DME molecules which leads to strong coordination. This leads to a change of the chemical shift of 7Li nuclei due to them being increasingly de-shielded. Interestingly, we found that the diffusivity of both Li+ and DME species are very similar, which also confirms that a Li-DME complex is present with FSI anion associated in the next coordination sphere to counterbalance the positively charged Li complex. MD simulations are underway to better elucidate the molecular shell structure of the system. We have also carried out electrochemical characterizations of these hybrid electrolytes to determine their potential applicability in a lithium sulphur battery. It was apparent using cyclic voltammogram (CV) performed in a three electrode set-up, that an increasing amount of DME increases the ionic conductivity but decreases the lithium plating-stripping efficiency. A coin-cell study of Li/Li symmetrical cycling showed an excellent plating-stripping behaviour for 70%IL-30%DME composition. We have carried out a full cell cycling against sulphur cathode and the optimised electrolyte composition obtained a promising first discharge capacity of 1100mAh/g. Additionally, we have investigated the sulphur speciation in the presence of this ionic liquid in a three-electrode system where platinum mesh has been used as working electrode coupled with in-situ UV-vis spectroscopy. Finally, a time dependent bulk electrolysis study revealed the plausible intermediates formed during the charge-discharge cycle of sulphur redox reaction. From these studies it appears that the composition of this novel hybrid electrolyte system can be tuned to provide a system with improved transport, electrochemical and sulphur speciation properties which lend themselves to a higher performance, next generation lithium sulphur battery technology.

A Mg-Doped High-Nickel Layered Oxide Cathode Enabling Safer, High-Energy-Density Li-Ion Batteries

High-nickel layered oxide cathodes with a Ni content of >90% show substantial potential for next-generation lithium-ion batteries (LIBs) due to their high capacity and lower cost. However, they are plagued by rapid capacity decay and poor thermal stability, which hamper their practical viability. We present here Li0.98Mg0.02Ni0.94Co0.06O2 (NC-Mg) with 2% Mg doping, aiming to provide a strategic guideline for solving the issues. The Mg2+ ions occupy the lithium layer and are proposed to act as pillar ions, which substantially enhance the structural reversibility and reduce the anisotropic lattice distortion upon cycling, thereby greatly improving the electrochemical and thermal stability of NC-Mg compared to the undoped LiNi0.94Co0.06O2 (NC). Specifically, NC-Mg delivers 214 mA h g–1 with a capacity retention of 80.1% after 500 cycles in pouch-type full cells, much higher than the retention of NC (56.3%). A discharge capacity of 158 mA h g–1 at 10C rate demonstrates its remarkable rate capability. Addition...

Synthesis of Single Crystal LiNi0.88Co0.09Al0.03O2 with a Two-Step Lithiation Method

Single crystal positive electrode materials for lithium-ion batteries have superior properties compared to their polycrystalline counterparts as has been demonstrated by industry and academia. Single crystal LiNi0.5Mn0.3Co0.2O2 (NMC532), NMC622 and now NMC811 have been successfully commercialized. However, single crystal LiNi1-x-yCoxAlyO2(NCA) materials have not been reported yet. One simple method for producing single crystal NMC material requiring high temperature and excess lithium during synthesis creates Li5AlO4 impurities if applied directly in attempts to synthesize single crystal NCA materials. This work introduces a two-step lithiation method for single crystal LiNi0.88Co0.09Al0.03O2 synthesis, which can prevent the formation of Li5AlO4 impurities. Powder X-ray diffraction, electron backscatter diffraction, and electrochemical measurements show the viability of the two-step lithiation method. Full coin cell cycling shows that the capacity retention of the single crystal NCA samples is at least as good as their polycrystalline counterparts. It is believed that this two-step lithiation method can be used for the synthesis of single crystal NCA and other single crystal Al-containing positive electrode materials. We believe this can lead to longer lived Li-ion cells with Ni-rich positive electrode materials.

Roll-to-roll prelithiation of Sn foil anode suppresses gassing and enables stable full-cell cycling of lithium ion batteries

LixSn foil anode prepared by mechanical prelithiation suppresses gassing and achieves stable full-cell cycling in lithium ion batteries.

Understanding the role of conductive polymer in thermal lithiation and battery performance of Li-Sn alloy anode

There is an urgent demand to develop high-capacity electrode materials for electric vehicles. LixSn alloy is one promising anode due to its pre-stored lithium and high capacity, but faces several challenges, especially high chemical reactivity and huge volume variation. Here, we conformally coated a conductive polypyrrole on the Sn nanoparticle, and first time studied the protection effect of the polymer on thermal lithiation process of the Sn nanoparticles. By tuning the thickness of polypyrrole from 8 to 40 nm, we find that the optimized coating layer (20 nm) keeps intact during the thermal lithiation, and ensures LixSn nanoparticles a very high stability in dry air condition. Moreover, the flexible and conductive polypyrrole accommodates huge volume variation of LixSn nanoparticles and enhances the electronic connections of interparticles. As a result, the LixSn@PPy (20 nm) composite maintains 75% of its prelithiated capacity after exposure to dry air for 5 days and delivers a stable reversible capacity of 534 mA h g-1 for 300 cycles. This anode material is also paired with traditional LiFePO4 cathode to achieve a stable full cell cycling.

The effect of Fe as an impurity element for sustainable resynthesis of Li[Ni1/3Co1/3Mn1/3]O2 cathode material from spent lithium-ion batteries

We synthesize Li[Ni1/3Co1/3Mn1/3]O2 (NCM) and Li[Ni1/3Co1/3Mn1/3]FexO2 (NCMF) cathode active materials with various amounts of Fe via hydroxide coprecipitation and calcination processes, which simulate the resynthesis of NCM in leach liquor containing Fe from spent lithium-ion batteries (LIBs). The crystal structure and electrochemical performances of the synthesized NCMF (i.e., NCMF (0.05%), NCMF (0.25%) and NCMF (1.0%)), are investigated and compared with NCM. The structural perfection of NCMF gradually deteriorates with increasing the amount of Fe because of undesirable cation mixing between Ni2+/Fe3+ and Li+ sites. In LIB performances, NCMF (0.05%) and NCMF (0.25%) present relatively reduced overpotential leading to superior rate performance at high C-rates to NCM with NCMF (1.0%) having the poorest. In terms of cycling stability, however, capacity retention improves as the Fe content in NCMF increases. The thermal stability of NCM and NCMF is also measured by differential scanning calorimetry, and the post-mortem analysis of X-ray photoelectron spectroscopy reveals that the ratio of Mn3+ becomes lower after cycling tests as the amount of Fe in NCMF increases. Moreover, the additional post-mortem analysis of energy dispersive spectroscopy on graphite surface after full cell cycling tests further confirms the positive effect of Fe on the improved capacity retention performance of NCMF. Therefore, even if Fe is regarded as an impurity component in the LIB recycling process, a small amount of Fe in the resynthesized NCM cathode material could favor high power and high cycling stability.

Superior full-cell cycling and rate performance achieved by carbon coated hollow Fe3O4 nanoellipsoids for lithium ion battery

Iron oxide, a promising anode material for lithium ion batteries, has a high theoretical specific capacity but exhibits poor cycling performance and rate capability. To resolve these issues, 150 nm sized carbon coated, hollow Fe3O4 nanoellipsoids are designed in this study. Owing to the relatively high utilization ratio of Fe3O4 and the buffer provided by the carbon layer, this composite has enhanced lithium ion storage properties and long cycle life. From half-cell measurements, the capacity is found to be in excess of 400 mAh g−1 even after 1000 cycles at 5 A g−1. And then, a facile and practical strategy is used to gain a relatively high compressed density (∼1.87 g cm−3), so the volumetric capacity of the Fe3O4@C electrode can be further enhanced by subjecting it to compression. In the full cell test, the Fe3O4@C electrode has a specific capacity of 400 mAh g−1 and volumetric capacity of 749 mAh cm−3 after 100 cycles. The improvement in cycling stability can be attributed to minimal volume expansion and the stability of the solid-electrolyte interphase (SEI) layer, over the nanoparticles. Finally, the evolution of solid-electrolyte interphase layer is indirectly monitored and the progressive loss of active lithium is quantitatively measured.

Thermal Stability of Fluoroethylene Carbonate (FEC) Containing Electrolytes Using LiPF6 As Conductive Salt

Lithium- and manganese-rich layered oxides, also referred to as high energy NCM (HE-NCM), are a promising class of materials for applications in future Li-ion batteries. Due to their high specific discharge capacity (~250 mAh/g) and the high operating voltage, the energy density of next-generation batteries could be increased using these materials [1]. However, using ethylene-carbonate (EC) based electrolytes with Li- and Mn-rich layered oxides (HE-NCM) leads to a rapid capacity decay, and in order to improve the lifetime of HE-/NCM//Graphite full-cells, EC has to be replaced by a different cyclic carbonate [2]. Thus, fluoroethylene carbonate (FEC) is commonly used as cyclic carbonate to replace EC when using HE-NCM. While FEC was shown to significantly improve the cycling stability of HE-NCM, it is suggested that residual FEC, used as co-solvent, reacts with LiPF6 conductive salt, leading to detrimental side reactions within the electrolyte [2-4]. This reaction was shown to be significantly enhanced at high temperature cycling, while the exact mechanism is still not clear [3]. As a first step, we will use on-line electrochemical mass spectrometry (OEMS [5]) to examine the chemical FEC degradation in presence of LiPF6, studying the gas evolution of LiPF6 (1.5 M) containing solutions of EC and FEC at different temperatures. Figure 1 shows the gas evolution of EC + 1.5M LiPF6 and FEC + 1.5M LiPF6, with the aim to quantify the thermal stability of the conductive salt with different cyclic carbonates. While POF3 evolution in EC starts only at temperatures >60°C, it can be clearly seen that POF3 evolution in an FEC solvent starts already at 25°C, indicating the decomposition of LiPF6 already at room temperature. By analyzing the gases evolved from these reactions we aim to get mechanistic insights on the degradation mechanisms of LiPF6 in combination with FEC. Furthermore, we will use full cell cycling and electrochemical impedance spectroscopy in order to get evidence about the practical effect of these reactions, which is investigated at 25°C and 45°C. For the analysis of the decomposition products, X-ray photoelectron spectroscopy (XPS) will be used to analyze products on the anode and the cathode, produced in EC and FEC containing electrolyte. Literature: [1] M. M. Thackeray, S.-H. Kang, C. S. Johnson, J. T. Vaughey, R. Benedek and S. A. Hackney, J. Mater. Chem. 17, 3112-3125 (2007). [2] T. Teufl, D. Pritzl, B. Strehle, H.A. Gasteiger and M. A. Mendez, manuscript in preparation. [3] K. Kim, I. Park, S.-Y. Ha, Y. Kim, M.-H. Woo, M.-H. Jeong, W.C. Shin, M. Ue, S.Y. Hong and N.-S. Choi, Electrochimica Acta 225, 358-368 (2017). [4] B. Aktekin, R. Younesi, W. Zipprich, C. Tengstedt, D. Brandell and K. Edström, J. Electrochem. Soc., 164(4), A942-A948 (2017). [5] N. Tsiouvaras, S. Meini, I. Buchberger and H. A. Gasteiger, J. Electrochem. Soc., 160(3), A471-A477 (2013). [6] M. Metzger, M. Egawa, S. Solchenbach, and H. A. Gasteiger, Meeting s, MA2017-02 (4), 272 (2017). Acknowledgement: The authors want to thank BASF SE for their financial support of this work. Figure 1: OEMS cell containing 240 μl electrolyte, without separator or electrodes. The temperature applied to the cell is shown in the upper panel and was increased from 25°C up to 80°C. The lower panel shows the signal measured for m/z = 85, which can be correlated to POF3, as well as PF5 [6]. Figure 1

Reactivity of Layered Oxide Surfaces with CO2 and Moisture

Layered Oxides such as NCM111 are state-of-the-art cathode active materials (CAMs) for commercial applications as well as promising candidates for even higher energy density batteries by raising the nickel content up to 80% (NCM811) and beyond.1 However, recent studies2–4 have demonstrated the high reactivity of Ni-rich CAMs with CO2 and moisture, which is highly problematic for industrial electrode manufacturing processes. In addition, the electrochemical performance of NCM811 is drastically deteriorated by CO2 and moisture induced surface contamination.5 We present an in-depth surface analysis by X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of NCM based cathode materials before and after exposure to CO2-containing atmospheres with high relative humidity. In addition, we study the extent of surface contamination by performing thermogravimetric analysis coupled with mass spectrometry (TGA-MS). The impact on cell performance is revealed by gassing analysis via on-line electrochemical mass spectrometry (OEMS) and full-cell cycling tests. The impact of the Ni content on the surface contamination of NCM type CAMs as well as the role of the Brunauer-Emmet-Teller (BET) surface area will be elucidated. A possible strategy to mitigate the reactivity of CAM surfaces with CO2 and H2O might be the chemical modification of active material surfaces using analogous approaches to those proposed in the literature.6–8 The effectiveness of such surface treatments to prevent surface contamination will be evaluated. Acknowledgements: This work is financially supported by the BASF SE Battery Research Network. References G. E. Blomgren, J. Electrochem. Soc., 164, A5019–A5025 (2017).I. A. Shkrob, J. A. Gilbert, P. J. Phillips, R. Klie, R. T. Haasch, J. Bareño and D. P. Abraham, J. Electrochem. Soc., 164, A1489–A1498 (2017)S. E. Renfrew and B. D. McCloskey, J. Am. Chem. Soc., 139, 17853-17860 (2017).N. V. Faenza, L. Bruce, Z. W. Lebens-Higgins, I. Plitz, N. Pereira, L. F. J. Piper and G. G. Amatucci, J. Electrochem. Soc., 164, A3727–A3741 (2017).R. Jung, R. Morasch, P. Karayaylali, K. Phillips, F. Maglia, C. Stinner, Y. Shao-Horn and H. A. Gasteiger, J. Electrochem. Soc., 165, A132–A141 (2018).J. Choi, J. Kim, K.-T. Lee, J. Lim, J. Lee and Y. S. Yun, Adv. Mater. Interfaces, 3, 4–9 (2016).E. M. Erickson, H. Sclar, F. Schipper, J. Liu, R. Tian, C. Ghanty, L. Burstein, N. Leifer, J. Grinblat, M. Talianker, J. S. Shin, J. K. Lampert, B. Markovsky, A. I. Frenkel and D. Aurbach, Adv. Energy Mater., 7, 1700708 1-10 (2017).Y. Su, S. Cui, Z. Zhuo, W. Yang, X. Wang and F. Pan, ACS Appl. Mater. Interfaces, 7, 25105–25112 (2015).

Lithiation Effect of the Poly(Acrylic Acid) Binders on the Silicon Anode of Lithium-Ion Batteries

The exploration for the next generation of anode materials in the lithium-ion batteries is a vital subject in the past few years due to the huge demand of high capacity batteries. Silicon (Si) stands out as a promising anode material due to its high theoretical specific capacity (4200 mAh/g), enviroment friendliness and low costs. However, Si nanoparticles (NPs) experience severe volume changes up to 300 % during the lithiation/delithiation process, which leads to dramatic particle degradation and thus capacity loss. Novel polymeric binders with enhanced mechanical properties have been identified as one effective approach to alleviate this issue, and some examples include carboxymethyl cellulose (CMC), alginate, and poly(acrylic acid) (PAA), etc. By using those binders, cell performance has been greatly improved as compared to the conventional polyvinylidene fluoride (PVDF) binder. Among those candidates, PAA outperforms others possibly due to its superior mechanical properties. In this report we have attempted to investigate the lithiation effect of the PAA binders. Lithiating PAA binders could benefit the electrode laminate processing as well as cycling performance. A commercially available PAA sample with a characterized Mn of 147 kDa was used in this study. By titrating with LiOH solution, we controlled the pH of 10 wt% PAA solutions as well as the lithiation ratio (Table 1). Those binder solutions were used to fabricate silicon/ graphite composite electrodes that composed of 10 % PAA, 73 % Hitachi MagE, 15 % Si NPs (NanoAmour, 70-130 nm), and 2 % Timcal C45. Half-cell cycling results (Figure 1) indicated that different lithiation of PAA binders has dramatic impact on their corresponding cycling performance. Lower lithiation tends to afford higher initial specific capacities and better capacity retentions. Actually, the best performer is PAA binder with no lithiation at all. This result is a little contradicting to previous study but we reason that our lithiation agent, LiOH, may have side reasons with silicon particles, as evidenced by the dramatic decrease of the silicon capacity. Full cell cycling as well as further characterization of electrode surface is ongoing. Table 1. The calculated mol% of LiOH (to AA monomer) and the resulting pH values of the final PAA solutions. LiOH % 0 25 50 75 85 90 91 92.5 95 100 pH 2.08 4.22 4.84 5.49 5.97 6.97 10.03 11.96 12.28 12.59 Figure 1. Specific discharge capacity and Coulombic efficiency of PAA binders with different pH values. Figure 1

In Situ Mass Spectrometry Studies of Gas Evolution Reactions During Cell Cycling in Aqueous Lithium Ion Batteries

In terms of safety, toxicity, cost and manufacturing simplicity, lithium ion batteries with aqueous electrolytes offer significant advantages over their non-aqueous counterparts. Despite these advantages, a low thermodynamic stability window of water (1.23 V, 2.62 V to 3.85 V vs. Li+/Li at pH 7) yields a low cell voltage, hence a low energy density system as compared to state-of-the-art non-aqueous Li-ion batteries. However, recent ‘water in salt’ (WiS),1 ‘water in bisalt’ (WiBS)2 and ‘hydrate melt’3 electrolytes widen the electrochemical stability window of water from 1.23V to >3.0V (~1.8 V to 5.0 V vs. Li+/Li), which results an energy density >100 Wh/kg when coupled a S-anode to a LiMn2O4 cathode.4 While these reports highlight impressive overall cell performances,1-4 gas evolution analyses of H2 at anode via HER and O2 at cathode via OER, or any other gas producing parasitic reaction, e.g. Li2S + 2H2O → H2S + 2LiOH @ S-anode, are not adequately addressed. At Liox, we anticipate that H2 and O2 generation from water electrolysis, or any other gas generating parasitic reaction would be detrimental to overall cell performance, and severely limit their ability to be practical and safe energy storage systems. To validate this conjecture, we have designed a special hermetically sealed Swagelok cell with known volume, comprising a high precision pressure sensor (Omega) and a three way Valco valve which can easily be connected to a high resolution mass spectrometer for qualitative and quantitative - in situ or ex situ - analysis of evolved gases during cell operation. We have tested a number of cathode and anode active materials – such as LFP, LMO, NMC, NCA, LCO, S, LTO, C-TiO2, etc. in the hermetically sealed cell. To study the cathode and anode separately, we assembled a series of symmetric cells; either cathode/cathode for OER or anode/anode for HER, and cycled them to monitor pressure changes, and identify and quantify the evolved gases by high precision RGA mass spectrometer. In this presentation, a series of symmetric and full-cell cycling data (>300 cycles) to discern gas evolving parasitic side reactions, pressure changes during cell operation, in situ and ex situ mass spectrometric analysis of evolved gases will be discussed.

Three-dimensional conductive network formed by carbon nanotubes in aqueous processed NMC electrode

Aqueous processing of lithium nickel manganese cobalt oxide (LiNi0.5Mn0.3Co0.2O2, NMC 532) cathodes was investigated by incorporating carbon nanotubes (CNTs) as the conductive additive. Morphology observation showed CNTs evenly disperse across the electrode, uniformly covering each primary particle, and form three-dimensional electronic pathways. A resistance measurement indicated the CNTs can improve the electronic conductivity of the composite electrode by an order of magnitude compared to carbon black. CNTs based electrodes showed higher rate performance, lower hysteresis, and better cycling performance with 99.4% capacity retention after 200 cycles in full pouch cells compared to 94.6% for carbon black based electrode. Meanwhile, the content of active materials in the electrode was increased from 90 wt% to 96 wt% and the energy density was increased by 11.7%. This research demonstrates an effective combined approach for achieving aqueous processed cathodes with enhanced durability while simultaneously achieving higher energy density by reducing the content of inactive components.

Reduced expansion and improved full-cell cycling of a SnOx#C embedded structure for lithium-ion batteries

Embedded SnOx#C composite, with excellent structural robustness, exhibits stable full-cell performance and enhanced gravimetric/volumetric capacity.

Lithium Metal Anodes: A Recipe for Protection

Effective stabilization of lithium metal anode is the key to the development of next-generation high-energy rechargeable batteries. In this issue of Joule, Linda Nazar and colleagues demonstrated a rationally designed electrolyte additive that can form a robust, single-ion-conducting protective layer on lithium metal surface while the battery operates, promoting uniform lithium deposition with high cycling efficiency.

The Adder Phenomenon Emerges from Independent Control of Pre- and Post-Start Phases of the Budding Yeast Cell Cycle

Although it has long been clear that cells actively regulate their size, the molecular mechanisms underlying this regulation have remained poorly understood. In budding yeast, cell size primarily modulates the duration of the cell-division cycle by controlling the G1/S transition known as Start. We have recently shown that the rate of progression through Start increases with cell size, because cell growth dilutes the cell-cycle inhibitor Whi5 in G1. Recent phenomenological studies in yeast and bacteria have shown that these cells add an approximately constant volume during each complete cell cycle, independent of their size at birth. These results seem to be in conflict, as the phenomenological studies suggest that cells measure the amount they grow, rather than their size, and that size control acts over the whole cell cycle, rather than specifically in G1. Here, we propose an integrated model that unifies the adder phenomenology with the molecular mechanism of G1/S cell-size control. We use single-cell microscopy to parameterize a full cell-cycle model based on independent control of pre- and post-Start cell-cycle periods. We find that our model predicts the size-independent amount of cell growth during the full cell cycle. This suggests that the adder phenomenon is an emergent property of the independent regulation of pre- and post-Start cell-cycle periods rather than the consequence of an underlying molecular mechanism measuring a fixed amount of growth.

Superior Shelf Life and Moisture Tolerance of ALD-Coated Cathode Materials As Important Aspect of ALD-Based Improvements of Li-Ion Cell Cycle Life

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 full cell cycle life. The changes in surface chemistry of ALD-coated cathode particles and their specific effects on electrochemical performance have not been studied in detail. Unmodified particle surfaces contain active oxygen, LiOH, and Li2CO3 species. The chemistry of these species during delithiation and interaction with the electrolyte can introduce components of impedance that can limit the capacity and rate capability of the material. Moisture adsorption can occur over time which can interact with and generate more of these species, causing a further deterioration of capacity. We have shown that important functions of ALD are to “clean” the particle surfaces, decreasing the content of LiOH and moisture, and forming a barrier to water adsorption and further generation of these species. Thus an important mechanism of ALD enhancement of cathode materials in full cells is demonstrated. This understanding should be applied to past and future studies, and represents a powerful new strategy to mitigate the effects of moisture.