Half-cell Cycling Research Articles

Self-limited and reversible surface hydration of Na2Fe(SO4)2 cathodes for long-cycle-life Na-ion batteries

Air stability is a crucial factor in the practical application of a battery material, as it profoundly affects the material's preparation, storage, and electrode fabrication processes. Sodium iron sulfate cathodes, despite their attractive attributes in cost and electrochemical performance, are widely believed to be unstable upon air exposure because of the sulfate group. Here we report remarkable air-stability of the Na2Fe(SO4)2-based (NFS) cathodes (minimal decay in 20 % RH air for 60 days, 91.9 % capacity retention after 3500 cycles in half cells) and their outstanding cycle performance in practically relevant pouch-type full cells (∼100 Wh kg-1 specific energy, >1000 cycle-life). Although the NFS cathodes do react with moisture H2O to produce Na2Fe(SO4)2⋅4H2O but the hydration is spatially confined at the NFS particles’ surface and not propagating into their bulk. Further, the structural changes are reversible when the surface-hydrated NFS particles are heated in the typical electrode vacuum-drying process, avoiding extra treatment and additional cost. This work reveals the promising properties of the NFS cathode materials towards high-performance and sustainable Na-ion batteries.

Oxidized Ti3Al(1-x)SnxC2 MAX phases as negative electrode materials for sodium ion batteries

Materials proposed for the negative electrodes in sodium-ion batteries often include oxides capable of reacting with Na+ through intercalation, conversion, or alloying. While these oxides offer high specific capacities, they suffer from poor mechanical stability. A novel approach to address this issue involves designing tailored nanocomposites based on the (Ti/Sn)Ox system, achieved through partial oxidation of tin-containing MAX phase (Ti3Al(1-x)SnxC2, x = 0.4 and 0.7). By employing this strategy, we have developed composite electrodes based on Ti(1-y)SnyO2 and MAX phase, which exhibit remarkable durability, withstanding over 600 cycles in half-cells. These electrodes also demonstrate charge efficiencies higher than 99.8 % and specific capacities comparable to MXenes electrodes. These outstanding electrochemical performances are further validated at the full-cell level when combined with Na0.44MnO2 positive electrodes. The reaction mechanism between the composite and the sodium ion was also studied using in-situ techniques (Raman and XAS) and the contribution of the different components during sodiation and de-sodiation was highlighted.

(Invited) MAX Phase Oxidation As a Novel Approach to Highly Reversible Oxide Nanocomposite Electrodes for Lithium-Ion Batteries

Among the materials utilized for the negative electrodes in Li-ion batteries, there is notable interest in oxides that can undergo reactions with Li+ through processes like intercalation, conversion, or alloying. These oxides exhibit high specific capacities but face challenges related to inadequate mechanical stability. A novel approach to constructing nanocomposites involves the partial oxidation of the tin-containing MAX phase within the Ti3Al(1-x)SnxO2 composition. By employing this strategy, and optimizing the Sn amount and the oxidation process, we have developed composite electrodes comprising Sn/TiOx and MAX phase, demonstrating exceptional durability with over 600 cycles in half cells. These electrodes exhibit charge efficiencies exceeding 99.5% and specific capacities comparable to graphite, surpassing those of lithium titanate (Li4Ti5O12) or MXene-based electrodes. These remarkable electrochemical performances extend to full cell configurations when combined with a low cobalt content layered oxide. The success of these electrodes is elucidated through a thorough chemical, morphological, and structural investigation, revealing the intimate contact between the MAX phase and oxide particles. Throughout the oxidation process, electroactive nanoparticles of TiO2 and Ti(1-y)SnyO2 emerge on the surface of the unreacted MAX phase, which serves both as a conductive agent and a buffer to maintain the mechanical integrity of the oxide during lithiation and de-lithiation cycles.

π-d Interaction to promote Zn ion de-solvation and transference toward high-performance Zn-MnO2 battery

Aqueous zinc ion batteries (AZIBs) are one class of high-safety and low-cost electrochemical energy storage devices supplementary to the current lithium ion technologies. However, their cycling performance has been severely tethered by the high de-solvation barrier of hydrated Zn ions and uncontrolled dendrite growth and side reactions on the Zn anodes. Herein, an artificial zincophilic passivation layer is constructed on the Zn anode surface by impregnating the porous Zn-based zeolitic imidazole frameworks (ZIF-8) with polypyrrole of rich π-electron donation. This not only lowers the de-solvation and nucleation barriers through π-d interaction, but also offers spatial room for accommodating 3D matrix Zn storage, lending smooth Zn plating/stripping with greatly improved kinetics in addition to inhibited dendrite formation and side reactions. Consequently, at 5 mA cm−2 the as-modified Zn anodes demonstrate a high CE of 99.6 % for more than 1500 cycles in half-cells and a stable operation for more than 2500 h in symmetrical cells. The aqueous Zn-MnO2 full cells further present a superb cycling performance with a capacity retention of 86.3 % after 1200 cycles at 1 A g−1. This work underscores the application of zincophilic and porous passivation layer to mediate smooth Zn plating/stripping by modulating the de-solvation and nucleation energy barriers.

Practical Alloy-Based Negative Electrodes for Na-ion Batteries

The volumetric capacity of typical Na-ion battery (NIB) negative electrodes like hard carbon is limited to less than 450 mAh cm−3. Alloy-based negative electrodes such as phosphorus (P), tin (Sn), and lead (Pb) more than double the volumetric capacity of hard carbon, all having a theoretical volumetric capacity above 1,000 mAh cm−3 in the fully sodiated state. These alloy materials have massive volume expansion, with P expanding by almost 300% and both Sn and Pb expanding to about 400% of their initial volumes when fully sodiated. This work shows that despite this large volume change, Sn and Pb have excellent half-cell cycling performance, including high Coulombic efficiency. A blended P-hard carbon cell shows promising initial performance despite P having far lower electronic conductivity than either Sn or Pb. Overall, it is expected that these Na-alloying elements will be needed to increase the volumetric energy density of NIBs to compete with low-cost lithium iron phosphate-based cells. In fact, one company, UNIGRID, has recently demonstrated cylindrical Na-ion cells that use a pure tin negative electrode, dramatically increasing the volumetric energy density of Na-ion technology.

A novel morphology of high voltage LiMn1.5Ni0.5O4 cathode material with niobium-doping

Spinel LiMn1.5Ni0.5O4 (LMNO) is one of the promising cathode materials for the next generation Li-ion batteries due to its voltage platform. However, the dissolution of the transition metal at high voltage is the biggest obstacle that LMNO suffers from. In this study, we successfully suppressed transition metal dissolution in LMNO by the morphology control from regular octahedron to spherical. Niobium was integrated as a dopant, which restricted the growth of (111) crystal face, and increased the indices of crystal faces by homogenizing the surface energy. By changing to a smaller surface area with spherical morphology, the contact area with the electrolyte was reduced, thus suppressing the dissolution of the Mn ion. Consequently, the niobium-doped LMNOexhibited superior rate performance, capacity retention with 74.1% at 1C after 500 cycles in half-cell, and thermal stability compared to pristine LMNO.

Enhanced electrochemical performance of LiNi0.6Co0.2Mn0.2O2 cathode for lithium ion batteries via a modified calcination process

Nickel (Ni)-rich cathodes with long service life and high energy density are play important role in the rapidly development of lithium ion batteries. However, the rapid development of Ni-rich cathode is still limited by its unstable structure and severely attenuated capacity. Herein, the LiNi0.6Co0.2Mn0.2O2 cathode was obtained from the solid phase method followed by calcination with a low-temperature holding step. The sample (LNCM-3) synthesized with calcination at 250 °C for 6 h and 850 °C for 10 h exhibits higher discharge specific capacity of 194.8 mAh g−1 and 131.0 mAh g−1 at 0.1C and 5C current density, and the capacity retention were 96.2 % and 75.7 % at 1C and 5C after 100 cycles in half cell. The obvious improved electrochemical performances are due to the low-temperature holding step could extend layer spacing and increase the crystalline of materials, which are confirmed by the results of XRD and TEM. Moreover, the full battery assembled with LNCM-3 as the cathode displays a higher specific capacity of 165.8 mAh g−1 at 0.1C and a superior cycling stability of 96.0 % after 100 cycles at 1C rate in the voltage range of 2.7–4.2 V.

Nonflammable Succinonitrile-Based Deep Eutectic Electrolyte for Intrinsically Safe High-Voltage Sodium-Ion Batteries.

Intrinsically safe sodium-ion batteries are considered as a promising candidate for large-scale energy storage systems. However, the high flammability of conventional electrolytes may pose serious safety threats and even explosions. Herein, a strategy of constructing a deep eutectic electrolyte is proposed to boost the safety and electrochemical performance of succinonitrile (SN)-based electrolyte. The strong hydrogen bond between S═O of 1,3,2-dioxathiolane-2,2-dioxide (DTD) and the α-H of SN endows the enhanced safety and compatibility of SN with Lewis bases. Meanwhile, the DTD participates in the inner Na+ sheath and weakens the coordination number of SN. The unique solvation configuration promotes the formation of robust gradient inorganic-rich electrode-electrolyte interphase, and merits stable cycling of half-cells in a wide temperature range, with a capacity retention of 82.8% after 800 cycles (25°C) and 86.3% after 100 cycles (60°C). Correspondingly, the full cells deliver tremendous improvement in cycling stability and rate performance.

Two‐dimensional sp2‐carbon‐linked covalent organic framework for large‐capacity and long‐life Na metal batteries

AbstractNa metal batteries are regarded as an encouraging route for energy‐dense and low‐cost battery systems. However, the unstable and irreversible Na plating/stripping, caused by the uncontrolled dendritic Na growth, prevents their practical applications. Herein, a two‐dimensional sp2‐carbon‐linked covalent organic framework (cyano‐sp2c‐COF) is adopted as seeding/hosting coating layer for a highly stable interface with long cycling life, large capacity, and high Na utilization. Benefit from the features of a fully π‐conjugated structure and well‐defined cyano groups, cyano‐sp2c‐COF with superior sodiophilicity and small interface resistance can reduce the nucleation barrier, enable Na ion flux uniformity, and enhance interface stability. Ultimately, the system achieves a low nucleation overpotential of only 10 mV, a remarkable average Coulombic efficiency of 99.7% maintained over 500 cycles in half cells, and exceptional interfacial durability of 8500 h with a high accumulated capacity of 8.5 Ah cm−2 in symmetric cells. Furthermore, the symmetric cells also present a steady cycling, even increasing the depth of discharge up to 90%. As proof, full cells demonstrate a long lifespan enduring 2700 cycles with tiny capacity decay, providing valuable insights into the long‐life Na batteries.

Enabling the use of lithium bis(trifluoromethanesulfonyl)imide as electrolyte salt for Li‐ion batteries based on silicon anodes and Li(Ni0.4Co0.4Mn0.2)O2 cathodes by salt additives

AbstractLithium bis(trifluoromethanesulfonyl)imide (LiFSI) is a promising alternative salt for Li‐ion batteries. Unlike the conventional LiPF6, it is not prone to HF formation, and thus resistant to moisture. However, for cell voltages relevant for high energy cathodes (>4.2 V), the aluminium current collector will corrode in electrolytes based on this salt, and mitigation strategies are needed. Here, the use of Lithium tetrafluoroborate (LiBF4) and Lithium difluoro(oxalato)borate (LiDFOB) salts as additives is investigated, in order to enable the use of LiFSI‐based electrolytes. The performance of the electrolytes is evaluated separately for high content silicon anodes, (NMC442) cathodes and the aluminium current collector by electrochemical methods and post mortem analysis by SEM imaging and X‐ray photoelectron spectroscopy (XPS). Electrolytes with LiDFOB as additive showed the best performance for all components, and were therefore selected for cycling in full cells, composed of silicon anodes and NMC442. Results show that LiFSI‐based electrolytes with LiDFOB additive has an electrochemical performance similar to conventional electrolytes, and is thus a competitive, alternative electrolyte with a low fluorine content. Furthermore, it is verified that the good SEI forming properties of LiFSI based electrolytes known from cycling in half cells, is also preserved during cycling in full cells

Unveiling the tailorable electrochemical properties of zeolitic imidazolate framework-derived Ni-doped LiCoO2 for lithium-ion batteries in half/full cells

As a prevailing cathode material of lithium-ion batteries (LIBs), LiCoO2 (LCO) still encounters the tricky problems of structural collapse, whose morphological engineering and cation doping are crucial for surmounting the mechanical strains and alleviating phase degradation upon cycling. Hereinafter, we propose a strategy using a zeolitic imidazolate framework (ZIF) as the self-sacrificing template to directionally prepare a series of LiNi0.1Co0.9O2 (LNCO) with tailorable electrochemical properties. The rational selection of sintering temperature imparts the superiority of the resultant products in lithium storage, during which the sample prepared at 700 °C (LNCO-700) outperforms its counterparts in cyclability (156.8 mA h g−1 at 1 C for 200 cycles in half cells, 1 C = 275 mA g−1) and rate capability due to the expedited ion/electron transport and the strengthen mechanical robustness. The feasibility of proper Ni doping is also divulged by half/full cell tests and theoretical study, during which LNCO-700 (167 mA h g−1 at 1 C for 100 cycles in full cells) surpasses LCO-700 in battery performance due to the mitigated phase deterioration, stabilized layered structure, ameliorated electronic conductivity, and exalted lithium storage activity. This work systematically unveils tailorable electrochemical behaviors of LNCO to better direct their practical application.

Building a robust surface structure toward stable ultrahigh-nickel cathodes

Ni-rich cathodes especially with Ni content over 90 % are promising next-generation cathode materials for advanced high energy lithium − ion batteries. However, in comparison with Ni ≤ 80 % Ni-rich cathodes, these ultrahigh Ni-rich materials face more severe challenges in terms of harmful H2 − H3 phase transformations and structural degradation during cycling. Herein, we present a robust surface structure composted of defect-rich disordered structures and LiF/Li2SiO3 coating for stabilizing the ultrahigh Ni-rich cathode LiNi0.96Co0.03Mn0.01O2 (NCM96) by modification with (NH4)2SiF6. The surface disordered structures including Li/TM mixing, spinel, and rock salt structure play a crucial role in inhibiting the irreversible H2-H3 phase transition and reducing lattice volume changes by lattice coherence effect. Moreover, the disordered surface in collaboration with the co-coating restrains the rapid growth of surface rock salt phase into the bulk, enhancing structural stability. The modified sample NSF-0.5 delivers a capacity of 238 mAh/g at 0.1C and maintains a capacity retention of 88.5 % at 0.5C after 100 cycles in half cell as well as 82.3 % at 1C after 300 cycles in full cell, significantly superior to the NCM96. The findings provide a simple and cost-effective surface modification strategy to enhance the structural stability and electrochemical performance of ultrahigh nickel cathodes for high-energy density LIBs.

Self‐Confinement of Na Metal Deposition in Hollow Carbon Tube Arrays for Ultrastable and High‐Power Sodium Metal Batteries

AbstractSodium metal batteries are promising next‐generation energy storage technology by using energy‐dense and affordable Na metal anodes, yet suffering uncontrollable Na dendritic growth issues. Herein, Au nanoparticle@hollow amorphous carbon tube yolk/shell arrays (Au/HCT‐CC) is rationally designed on carbon cloth as a dynamic host. In situ transmission electron microscopy observations reveal a regulated dendrite‐free Na metal plating/stripping within the Au/HCT‐CC host. The self‐confinement of Na metal deposition in the hollow carbon can further stabilize the electrolyte/electrode interface and homogenize Na ion flux, as evidenced by rigorous experimental and theoretical characterizations, thus successfully accommodating the hurdles to Na metal anodes. When cycling in half cells, the Au/HCT‐CC electrodes deliver remarkably high coulombic efficiencies (CEs) of 99.96% over 2200 h at 5 mA cm−2. The high CE of 99.54% is preserved even under harsh cycling conditions of 10 mA cm−2 and 20 mAh cm−2 for 250 cycles. These values rival the state‐of‐the‐art electrochemical performance for Na metal anodes in literature. Finally, the practical feasibility of the new anode is demonstrated by cycling in Na3V2(PO4)3@C||Na‐Au/HCT‐CC full cells over 900 cycles with an extremely low capacity degradation rate of 0.017% per cycle.

Phosphonium-Based Ionic Liquid Electrolyte in Combination with Silicon Anodes and LiNi0.5-XMn1.5+XO4 Cathodes for Lithium Ion Batteries

Ionic liquids, like bis(fluorosulfonyl)imide (FSI) ionic liquids, are promising solvents for lithium ion batteries due to their high thermal stability and wide electrochemical window. The performance of ionic liquid electrolytes is however hampered by the low conductivity at room temperature, but the high thermal stability allows for operation at elevated temperatures, at which the conductivity is significantly improved.Electrolytes based on LiFSI and ionic liquids of the cations; pyrrolidinium (PYR13 +), and phosphonium (P111i4 +), with FSI anions, have been shown to exhibit stable cycling at room temperature, and good rate performance for cells composed of silicon anodes and LiFePO4 cathodes at 60 °C [1,2]. The lithium ion mobilities, relative to standard carbonate electrolytes, were determined from the limiting current densities at room temperature and 60 °C. Significant differences in the temperature dependence of the transport properties were revealed, with a considerable increase in the lithium ion mobility from 20 to 60 °C for electrolytes based on P111i4FSI. The best rate performance at 60 °C was demonstrated for the P111i4FSI based electrolyte, with discharge capacities around 1000 mAh/gSi at a 2C rate [2]. The improved performance was attributed to a combination of the improved lithium ion mobility and formation of a more conductive solid electrolyte interphase (SEI) for this electrolyte.In view of the excellent high temperature performance of P111i4FSI, including high thermal stability and a large electrochemical window [1,2], this electrolyte has been selected for further studies as electrolyte for high voltage LiNi0.5-xMn1.5+xO4 (LNMO) cathodes. LiNi0.5-xMn1.5+xO4 (LNMO) is an attractive candidate as a next generation Li-ion battery (LIB) cathode material because it has a high energy density, due to the high operating voltage, and a relatively low cost (Co-free) compared to alternative cathode chemistries. However, the stability of LNMO is not yet satisfactory for commercial applications, especially in full-cell configuration with graphite as the anode material, and at elevated temperatures. One challenge is the transition metal (TM) dissolution, which poisons the graphite anode by degrading the solid electrolyte interface (SEI) [4]. The TM dissolution is affected by the formation of hydrofluoric (HF) acid in carbonate-based electrolytes utilizing the LiPF6 salt [3]. Additionally, the decomposition processes occur with an increased rate at elevated temperatures [4,5]. Another challenge is the side reactions occurring at the high operating voltage, which limits the coulombic efficiency. Previous works have indicated that the carbon conductive additive is more prone to side reactions than the LNMO active material [6].Here, we present a study on the phosphonium-based ionic liquid P111i4FSI, with two different salt concentrations: 0.79 m LiFSI and 3.0 m LiFSI, as an alternative electrolyte for LIBs with an LNMO cathode.The focus of the research is to study the side reactions separately on the carbon conductive additive, and on the LNMO active material. Carbon conductive additives differing in structure and particle size are studied. The electrolyte is tested both in half-cell and full-cell configuration with a graphite anode, as well as at room temperature and elevated temperatures. Using 0.79 m LiFSI P111i4FSI results in similar capacity retention, but higher coulombic efficiencies after 200 cycles in half-cells at room temperature compared to 1 M LiPF6 in 1:1 EC:DEC (v/v). Post-mortem characterization is carried out with SEM, TEM, Raman spectroscopy, and FT-IR.

Highly Reversible Ti/Sn Oxide Nanocomposite Electrodes for Lithium Ion Batteries Obtained by Oxidation of Ti3 Al(1-x) Snx C2 Phases.

Among the materials for the negative electrodes in Li-ion batteries, oxides capable of reacting with Li+ via intercalation/conversion/alloying are extremely interesting due to their high specific capacities but suffer from poor mechanical stability. A new way to design nanocomposites based on the (Ti/Sn)O2 system is the partial oxidation of the tin-containing MAX phase of Ti3 Al(1-x) Snx O2 composition. Exploiting this strategy, this work develops composite electrodes of (Ti/Sn)O2 and MAX phase capable of withstanding over 600 cycles in half cells with charge efficiencies higher than 99.5% and specific capacities comparable to those of graphite and higher than lithium titanate (Li4 Ti5 O12 ) or MXenes electrodes. These unprecedented electrochemical performances are also demonstrated at full cell level in the presence of a low cobalt content layered oxide and explained through an accurate chemical, morphological, and structural investigation which reveals the intimate contact between the MAX phase and the oxide particles. During the oxidation process, electroactive nanoparticles of TiO2 and Ti(1-y) Sny O2 nucleate on the surface of the unreacted MAX phase which therefore acts both as a conductive agent and as a buffer to preserve the mechanical integrity of the oxide during the lithiation and delithiation cycles.

Impact of Calcium on Air Stability of Na[Ni1/3Fe1/3Mn1/3]O2 Positive Electrode Material for Sodium-ion Batteries

O3-type Na[Ni1/3Fe1/3Mn1/3]O2 is a promising positive electrode material for sodium-ion batteries. However, it suffers from structural degradation accompanied by surface-impurity growth during ambient storage and processing. In this study, we synthesized Na1–2yCay[Ni1/3Fe1/3Mn1/3]O2 with y = 0 and 0.02, and studied their structural stability towards ambient exposure. Na0.96Ca0.02[Ni1/3Fe1/3Mn1/3]O2 demonstrated excellent air stability by retaining 0.93 of lattice Na in the original O3 structure after 6 days of ambient storage. Titration experiments confirmed that the presence of Ca in Na0.96Ca0.02[Ni1/3Fe1/3Mn1/3]O2 effectively suppressed the otherwise rigorous Na+/H+ ion exchange in the presence of water. Charge/discharge cycling in half cells suggested that Ca improved the active material’s specific capacity and capacity retention by retaining its structural integrity and eliminating surface impurity formation during ambient electrode processing. Finally, the cycling performance of Na0.96Ca0.02[Ni1/3Fe1/3Mn1/3]O2/hard carbon full cells was evaluated with upper cut-off voltages of 4.0 V and 4.1 V. Raising the upper cut-off voltage to 4.1 V resulted in a 20% gain in specific energy, but also accelerated capacity fade and voltage polarization, most likely due to an irreversible phase transition above 4.0 V.

High Energy Density Li/Ni/Co‐Free O3/P2 Sodium Layered Oxide Intergrowth for Sodium‐Ion Batteries

AbstractSodium‐ion batteries have attracted widespread interest due to the potential for providing safe and cheap energy storage. However, large scale use of sodium‐ion batteries is limited by insufficient performance from positive electrode materials, while also avoiding the use of expensive and toxic elements. Here, we present a bi‐phasic sodium layered oxide material, O3/P2‐Na0.75Mn0.35Fe0.35Ti0.1Al0.1Cu0.1O2, free of Li, Ni, and Co, which delivered high energy densities up to 420 Wh kg−1, discharge potential of 3.03 V, and high capacity retention of 80 % over 70 cycles in half cells (292 Wh kg−1 in full cells). Crucially, the high Na content is sufficient to provide high energy densities in full cell format. The intergrown nature of the material was confirmed by TEM and SAED analysis, while ex‐situ XRD studies revealed the two phases undergo complementary c‐parameter evolution, reducing overall volume change. These results demonstrate the potential for future commercialisation of bi‐phasic materials utilizing only Earth abundant elements.

Understanding the Influence of Li7La3Zr2O12 Nanofibers on Critical Current Density and Coulombic Efficiency in Composite Polymer Electrolytes.

Composite polymer electrolytes (CPEs) are attractive materials for solid-state lithium metal batteries, owing to their high ionic conductivity from ceramic ionic conductors and flexibility from polymer components. As with all lithium metal batteries, however, CPEs face the challenge of dendrite formation and propagation. Not only does this lower the critical current density (CCD) before cell shorting, but the uncontrolled growth of lithium deposits may limit Coulombic efficiency (CE) by creating dead lithium. Here, we present a fundamental study on how the ceramic components of CPEs influence these characteristics. CPE membranes based on poly(ethylene oxide) and lithium bis(trifluoromethanesulfonyl)imide (PEO-LiTFSI) with Li7La3Zr2O12 (LLZO) nanofibers were fabricated with industrially relevant roll-to-roll manufacturing techniques. Galvanostatic cycling with lithium symmetric cells shows that the CCD can be tripled by including 50 wt % LLZO, but half-cell cycling reveals that this comes at the cost of CE. Varying the LLZO loading shows that even a small amount of LLZO drastically lowers the CE, from 88% at 0 wt % LLZO to 77% at just 2 wt % LLZO. Mesoscale modeling reveals that the increase in CCD cannot be explained by an increase in the macroscopic or microscopic stiffness of the electrolyte; only the microstructure of the LLZO nanofibers in the PEO-LiTFSI matrix slows dendrite growth by presenting physical barriers that the dendrites must push or grow around. This tortuous lithium growth mechanism around the LLZO is corroborated with mass spectrometry imaging. This work highlights important elements to consider in the design of CPEs for high-efficiency lithium metal batteries.

Confined Assembly of Hydrated Vanadium Oxide into Hollow Mesoporous Carbon Nanospheres for Fast and Stable K+ Storage Capability.

The rational structural design of the electrode materials is significant to enhance the electrochemical performance for potassium ion storage, benefiting from the shortened ion diffusion distance, increased conductivity, and pseudo-capacitance promotion. Herein, hydrated vanadium oxide (HVO) nanosheets with enriched oxygen defects are well confined into hollow mesoporous carbon spheres (HMCS), producing Od -VOH@C nanospheres through one-step hydrothermal reaction. Attributed to the restricted growth in the HMCS, the HVO nanosheets are loosely packed, generating abundant interfacial boundaries and large specific areas. As a result, Od -VOH@C nanospheres show increased reaction kinetics and well buffer the volume effects for the K+ storage. Od -VOH@C delivers stable capacities of 138 mAh g-1 at 2.0 A g-1 over 10000 cycles in half-cells attributed to the high pseudo-capacitance contribution. The K+ storage mechanism of insertion and conversion reaction is confirmed by ex situ X-ray diffraction, Raman, and X-ray photoelectron spectroscopy analyses. Moreover, the symmetric potassium-ion capacitors of Od -VOH@C//Od -VOH@C deliver a high energy density of 139.6Wh kg-1 at the power density of 948.3W kg-1 .

Interphase formation with carboxylic acids as slurry additives for Si electrodes in Li-ion batteries. Part 2: a photoelectron spectroscopy study

Preparing aqueous silicon slurries in presence of a low-pH buffer improves the cycle life of silicon electrodes considerably because of higher reversibility of the alloying process and higher resilience towards volume changes during (de)alloying. While the positive effects of processing at low pH have been demonstrated repeatedly, there are gaps in understanding of the buffer’s role during the slurry preparation and the effect of buffer residues within the electrode during cycling. This study uses a combination of soft and hard x-ray photoelectron spectroscopy to investigate the silicon particle interface after aqueous processing in both pH-neutral and citrate-buffered environments. Further, silicon electrodes are investigated after ten cycles in half-cells to identify the processing-dependant differences in the surface layer composition. By tuning the excitation energy between 100 eV and 7080 eV, a wide range of probing depths were sampled to vertically map the electrode surface from top to bulk. The results demonstrate that the citrate-buffer becomes an integral part of the surface layer on Si particles and is, together with the electrode binder, part of an artificial solid-electrolyte interphase that is created during the electrode preparation and drying.