Alternative electrochemical energy storage: potassium-based dual-graphite batteries

In this contribution, we report for the first time a novel potassium ion-based dual-graphite battery concept (K-DGB), applying graphite as the electrode material for both the anode and cathode. The presented dual-graphite cell utilizes a potassium ion containing, ionic liquid (IL)-based electrolyte, synergetically combining the extraordinary properties of potassium, graphite and ILs in terms of cost effectiveness, sustainability and safety. The IL electrolyte shows a very stable cycling performance in combination with the graphite anode at a so far not reported reversible capacity of ≈230 mA h g−1. A highly reversible capacity of >42 mA h g−1 (with respect to the graphite cathode) even at a current of 250 mA g−1, and a Coulombic efficiency (CE) exceeding 99% in a potential range from 3.4 V to 5.0 V vs. K/K+ represent the corner pillars of this innovative battery technology. The very promising electrochemical performance is further emphasized by a capacity retention of 95% after 1500 cycles. Furthermore, the electrochemical formation of a stage-1 potassium graphite intercalation compound (K-GIC) from an IL electrolyte, resulting in a stoichiometry of KC8 is presented in this work for the first time. The presented results shed new light on an alternative energy storage technology, especially in view of stationary (“grid”) energy storage by employing environmentally friendly, abundant and recyclable materials

Towards high-performance dual-graphite batteries using highly concentrated organic electrolytes

Dual-ion batteries (DIBs) and dual-graphite batteries (DGBs) attract increasing attention as an alternative approach for stationary energy storage due to their environmental, cost and safety benefits over other state-of-the-art battery technologies. In order to realize an extraordinary cell performance of DGBs, it is of particular importance to stabilize the interphases between electrolyte and electrode, for both the negative and positive electrodes. In this work, we present the implementation of highly concentrated electrolytes (HCEs) in DIBs and DGBs, i.e. electrolyte formulations based on either LiPF6 or LiTFSI in dimethyl carbonate (DMC), diethyl carbonate (DEC) or ethyl methyl carbonate (EMC). A reversible cycling stability of the graphitic negative electrode is proven as well as the stability of the HCEs against oxidative decomposition at the positive electrode at a cathode potential of 5V vs. Li/Li+. Additionally, we demonstrate that the anodic dissolution of the aluminum (Al) current collector is successfully suppressed by using LiTFSI-based HCEs, which show a comparable resistivity against Al dissolution as LiPF6-based electrolytes. Furthermore, a strong dependence of concentration and onset potential of anion intercalation is observed and comprehensively discussed with respect to the thermodynamic environment of the electrolyte. Overall, the use of HCEs enables a highly reversible cycling stability, providing extraordinary high specific discharge capacities of 80–100 mAh g−1 for lithium metal-based DIBs and DGBs. The evaluation of voltage efficiency (VE) and energy efficiency (EE) reveals the highest values for the EMC/LiPF6-based electrolyte, i.e. 96% (VE) and 95% (EE). In summary, the use of HCEs is a promising strategy to further optimize the electrochemical performance of DIBs and DGBs in terms of high reversible capacity and cycling stability and decreased parasitic side reactions

Ionic liquid-assisted solvothermal synthesis of hollow Mn2O3 anode and LiMn2O4 cathode materials for Li-ion batteries

Mn-based Mn2O3 anode and LiMn2O4 cathode materials are prepared by a solvothermal method combined with post annealing process. Environmentally friendly ionic liquid 1-Butyl-3-methylimidazolium tetrafluoroborate as both structure-directing agent and fluorine source is used to prepare hollow polyhedron MnF2 precursor. Both target materials Mn2O3 anode and LiMn2O4 cathode have the morphology of the MnF2 precursor. The Mn2O3 anode using carboxymethyl cellulose as binder could deliver slight better electrochemical performance than the one using poly (vinyldifluoride) as binder. The former has an initial charge capacity of 800 mAh g-1 at a current density of 101.8 mA g-1, and exhibits no obvious capacity decay for 150 cycles at 101.8 mA g-1. The LiMn2O4 cathode material prepared with molten salt assistant could display much better electrochemical performance than the one prepared without molten salt assistance. In particular, it has an initial discharge capacity of 117.5 mAh g-1 at a current density of 0.5C and good rate capability. In the field of lithium ion batteries, both the Mn2O3 anode and LiMn2O4 cathode materials could exhibit enhanced electrochemical performance due to the well formed morphology based on the ionic liquid-assisted solvothermal method

Development of Safe and Sustainable Dual-Ion Batteries Through Hybrid Aqueous/Nonaqueous Electrolytes

In this study, a new dual-ion battery (DIB) concept based on an aqueous/non-aqueous electrolyte is reported, combining high safety in the form of a nonflammable water-in-salt electrolyte, a high cathodic stability by forming a protective interphase on the negative electrode (non-aqueous solvent), and improved sustainability by using a graphite-based positive electrode material. Far beyond the anodic stability limit of water, the formation of a stage-2 acceptor-type graphite intercalation compound (GIC) of bis(trifluoromethanesulfonyl) imide (TFSI) anions from an aqueous-based electrolyte is achieved for the first time, as confirmed by ex-situ X-ray diffraction. The choice of negative electrode material shows a huge impact on the performance of the DIB cell chemistry, i.e., discharge capacities up to 40 mAh g−1 are achieved even at a high specific current of 200 mA g−1. In particular, lithium titanium phosphate (LiTi2(PO4)3; LTP) and lithium titanium oxide (Li4Ti5O12; LTO) are evaluated as negative electrodes, exhibiting specific advantages for this DIB setup. In this work, a new DIB storage concept combining an environmentally friendly, transition-metal-free, abundant graphite positive electrode material, and a nonflammable water-based electrolyte is established, thus paving the path toward a sustainable and safe alternative energy storage technology

Triphenylphosphine Oxide as Highly Effective Electrolyte Additive for Graphite/NMC811 Lithium Ion Cells

Nickel-rich layered oxide materials (LiNixMnyCo1–x–yO2, x ≥ 0.8, LiNMC) attract great interest for application as positive electrode in lithium ion batteries (LIBs) due to high specific discharge capacities at moderate upper cutoff voltages below 4.4 V vs Li/Li+. However, the comparatively poor cycling stability as well as inferior safety characteristics prevent this material class from commercial application so far. Against this background, new electrolyte formulations including additives are a major prerequisite for a sufficient electrochemical performance of Ni-rich NMC materials. In this work, we introduce triphenylphosphine oxide (TPPO) as electrolyte additive for the application in graphite/LiNi0.8Mn0.1Co0.1O2 (NMC811) cells. The addition of only 0.5 wt % TPPO into a carbonate-based electrolyte (LiPF6 in EC:EMC) significantly increases the first cycle Coulombic efficiency as well as the reversible specific capacity and improves the capacity retention of the LIB full cell cycled between 2.8 and 4.3 V. Electrochemical results indicate that the full cell capacity fade is predominantly caused by active lithium loss at the negative electrode. In this contribution, X-ray photoelectron spectroscopy and inductively coupled plasma-mass spectrometry analysis confirm the participation of the electrolyte additive in the solid electrolyte interphase formation on the negative electrode as well as in the cathode electrolyte interphase formation on the positive electrode, thus, effectively reducing the active lithium loss during cycling. Furthermore, the performance of the TPPO additive is compared to literature known electrolyte additives including triphenylphosphine, vinylene carbonate, and diphenyl carbonate demonstrating the outstanding working ability of TPPO in graphite/NMC811 cells

Triphenylphosphine Oxide as Highly Effective Electrolyte Additive for Graphite/NMC811 Lithium Ion Cells

Nickel-rich layered oxide materials (LiNi_<i>x</i>Mn_<i>y</i>Co_{1–<i>x</i>–<i>y</i>}O₂, <i>x</i> ≥ 0.8, LiNMC) attract great interest for application as positive electrode in lithium ion batteries (LIBs) due to high specific discharge capacities at moderate upper cutoff voltages below 4.4 V vs Li/Li⁺. However, the comparatively poor cycling stability as well as inferior safety characteristics prevent this material class from commercial application so far. Against this background, new electrolyte formulations including additives are a major prerequisite for a sufficient electrochemical performance of Ni-rich NMC materials. In this work, we introduce triphenylphosphine oxide (TPPO) as electrolyte additive for the application in graphite/LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cells. The addition of only 0.5 wt % TPPO into a carbonate-based electrolyte (LiPF₆ in EC:EMC) significantly increases the first cycle Coulombic efficiency as well as the reversible specific capacity and improves the capacity retention of the LIB full cell cycled between 2.8 and 4.3 V. Electrochemical results indicate that the full cell capacity fade is predominantly caused by active lithium loss at the negative electrode. In this contribution, X-ray photoelectron spectroscopy and inductively coupled plasma-mass spectrometry analysis confirm the participation of the electrolyte additive in the solid electrolyte interphase formation on the negative electrode as well as in the cathode electrolyte interphase formation on the positive electrode, thus, effectively reducing the active lithium loss during cycling. Furthermore, the performance of the TPPO additive is compared to literature known electrolyte additives including triphenylphosphine, vinylene carbonate, and diphenyl carbonate demonstrating the outstanding working ability of TPPO in graphite/NMC811 cells