Unveil the origin of voltage oscillation for sodium-ion batteries operating at -40 °C.

Voltage oscillation at subzero in sodium-ion batteries (SIBs) has been a common but overlooked scenario, almost yet to be understood. For example, the phenomenon seriously deteriorates the performance of Na3V2(PO4)3 (NVP) cathode in PC (propylene carbonate)/EC (ethylene carbonate)-based electrolyte at -20 °C. Here, the correlation between voltage oscillation, structural evolution, and electrolytes has been revealed based on theoretical calculations, in-/ex-situ techniques, and cross-experiments. It is found that the local phase transition of the Na3V2(PO4)3 (NVP) cathode in PC/EC-based electrolyte at -20 °C should be responsible for the oscillatory phenomenon. Furthermore, the low exchange current density originating from the high desolvation energy barrier in NVP-PC/EC system also aggravates the local phase transformation, resulting in severe voltage oscillation. By introducing the diglyme solvent with lower Na-solvent binding energy, the voltage oscillation of the NVP can be eliminated effectively at subzero. As a result, the high capacity retentions of 98.3% at -20 °C and 75.3% at -40 °C are achieved. The finding provides insight into the abnormal SIBs degradation and brings the voltage oscillation behavior of rechargeable batteries into the limelight.

Unlocking Fast Potassium Ion Kinetics: High-Rate and Long-Life Potassium Dual-Ion Battery for Operation at -60 °C.

Energy storage devices operating at low temperatures are plagued by sluggish kinetics, reduced capacity, and notorious dendritic growth. Herein, novel potassium dual-ion batteries (PDIBs) capable of superior performance at -60 °C, and fabricated by combining MXenes and polytriphenylamine (PTPAn) as the anode and cathode, respectively, are presented. Additionally, the reason for the anomalous kinetics of K+ (faster at low temperature than at room temperature) on the Ti3C2 anode is investigated. Theoretical calculations, crossover experiments, and in situ XRD at room and low temperatures revealed that K+ tends to bind with solvent molecules rather than anions at subzero temperatures, which not only inhibits the participation of PF6 - in the formation of the solid electrolyte interphase (SEI), but also guarantees co-intercalation behavior and suppresses undesirable K+ storage. The advantageous properties at low temperatures endow the Ti3C2 anode with fast K+ kinetics to unlock the outstanding performance of PDIB at ultralow temperatures. The PDIBs exhibit superior rate capability and high capacity retention at -40 °C and -60 °C. Impressively, after charging-discharging for 20,000 cycles at -60 °C, the PDIB retained 86.7 % of its initial capacity. This study reveals the influence of temperatures on MXenes and offers a unique design for dual-ion batteries operating at ultralow temperatures.

Constructing Stable Anion-Tuned Electrode/Electrolyte Interphase on High-Voltage Na3 V2 (PO4 )2 F3 Cathode for Thermally-Modulated Fast-Charging Batteries.

Constructing stable electrode/electrolyte interphase with fast interfacial kinetics is vital for fast-charging batteries. Herein, we investigate the interphase that forms between a high-voltage Na3 V2 (PO4 )2 F3 cathode and the electrolytes consisting of 3.0, 1.0, or 0.3 M NaClO4 in an organic carbonate solvent (47.5 : 47.5 : 5 mixture of EC: PC: FEC) during charging up to 4.5 V at 55 °C. It is found that a higher anion/solvent ratio in electrolyte solvation structure induces anion-dominated interphase containing more inorganic species and more anion derivatives (Cx ClOy ), which leads to a larger interfacial Na+ transport resistance and more unfavorable gas evolution. In comparison, a low anion/solvent ratio derives stable anion-tuned interphase that enables better interfacial kinetics and cycle ability. Importantly, the performance of a failed cathode is restored by triggering the decomposition of Cx ClOy species. This work elucidates the role of tuning interphase in fast-charging batteries.

Pseudocapacitance of TiO2-x /CNT Anodes for High-Performance Quasi-Solid-State Li-Ion and Na-Ion Capacitors.

It is challenging for flexible solid-state hybrid capacitors to achieve high-energy-high-power densities in both Li-ion and Na-ion systems, and the kinetics discrepancy between the sluggish faradaic anode and the rapid capacitive cathode is the most critical issue needs to be addressed. To improve Li-ion/Na-ion diffusion kinetics, flexible oxygen-deficient TiO2-x /CNT composite film with ultrafast electron/ion transport network is constructed as self-supported and light-weight anode for a quasi-solid-state hybrid capacitor. It is found that the designed porous yolk-shell structure endows large surface area and provides short diffusion length, the oxygen-deficient composite film can improve electrical conductivity, and enhance ion diffusion kinetic by introducing intercalation pseudocapacitance, therefore resulting in advance electrochemical properties. It exhibits high capacity, excellent rate performance, and long cycle life when utilized as self-supported anodes for Li-ion and Na-ion batteries. When assembled with activated carbon/carbon nanotube (AC/CNT) flexible cathode, using ion conducting gel polymer as the electrolyte, high energy densities of 104 and 109 Wh kg-1 are achieved at 250 W kg-1 in quasi-solid-state Li-ion and Na-ion capacitors (LICs and SICs), respectively. Still, energy densities of 32 and 36 Wh kg-1 can be maintained at high power densities of 5000 W kg-1 in LICs and SICs.

Carbon-reinforced Ni3S2/Ti3C2Tx MXene composite as an anode for superior-performance lithium-ion capacitors.

Lithium ion capacitors (LICs) are a new generation of energy storage devices that combine the super energy storage capability of lithium ion batteries with the satisfactory power density of supercapacitors. The development of high-performance LICs still faces great challenges due to the unbalanced reaction kinetics at the anode and cathode. Therefore, it is an inevitable need to enhance the electron/ion transfer capability of the anode materials. In this paper, to obtain a superior-rate and high-capacity Ni3S2-based anode, highly conductive Ti3C2Tx MXene sheets were introduced to sever as the carrier of Ni3S2 nanoparticles and simultaneously an amorphous carbon layer which coats onto the surface of Ni3S2 nanoparticles was in-situ generated by the carbonization of dopamine reactant. The as-synthesized Ni3S2/Ti3C2Tx/C composite exhibits a high specific surface area (112.6 m2/g) because of the addition of Ti3C2Tx that can reduce the aggregation of Ni3S2 nanoparticles and the in-situ generated amorphous carbon layer that can suppress the growth of Ni3S2 nanoparticles. The Ni3S2/Ti3C2Tx/C anode possesses a remarkable reversible discharge specific capacity (626.0 mAh/g under 0.2 A/g current density), which increases to 1150.8 mAh/g after 400-cycle charge/discharge measurement at the same measurement condition indicating eminent cyclability, along with superior rate capability. To construct a superior-performance LIC device, a sterculiae lychnophorae derived porous carbon (SLPC) cathode with an average discharge specific capacity of 73.4 mAh/g@0.1A/g was prepared. The Ni3S2/Ti3C2Tx/C//SLPC LIC device with optimal cathode/anode mass ratio has a satisfactory energy density ranging from 32.8 to 119.1 Wh kg-1 at the corresponding power density of 8799.4 to 157.5 W kg-1, together with a prominent capacity retention (95.5 %@1 A/g after 10,000 cycles).

A Cable-Stayed Honeycomb Superstructure to Improve the Stability of Li-Rich Materials via Inhibiting Interlaminar Lattice Strain.

In layered Li-rich materials, over stoichiometric Li forms an ordered occupation of LiTM6 in transition metal (TM) layer, showing a honeycomb superstructure along [001] direction. At the atomic scale, the instability of the superstructure at high voltage is the root cause of problems such as capacity/voltage decay of Li-rich materials. Here a Li-rich material with a high Li/Ni disorder is reported, these interlayer Ni atoms locate above the honeycomb superstructure and share adjacent O coordination with honeycomb TM. These Ni─O bonds act as cable-stayed bridge to the honeycomb plane, and improve the high-voltage stability. The cable-stayed honeycomb superstructure is confirmed by in situ X-ray diffraction to have a unique cell evolution mechanism that it can alleviate interlaminar lattice strain by promoting in-plane expansion along a-axis and inhibiting c-axis stretching. Electrochemical tests also demonstrate significantly improved long cycle performance after 500 cycles (86% for Li-rich/Li half cell and 82% for Li-rich/Si-C full cell) and reduced irreversible oxygen release. This work proves the feasibility of achieving outstanding stability of lithium-rich materials through superstructure regulation and provides new insights for the development of the next-generation high-energy-density cathodes.

A reversible redox strategy for SWCNT-based supercapacitors using a high-performance electrolyte.

In order to achieve pesudocapacitive performance of single-wall carbon nanotube (SWCNT) electrodes, a high-efficient and reversible redox strategy utilizing a redox-mediated electrolyte for SWCNT-based supercapacitors is reported. In this novel redox-mediated electrolyte, the single-electrode specific capacitance of the supercapacitor is heightened four times, reaching C=162.66 F g(-1) at 1 A g(-1). The quick charge-discharge ability of the supercapacitor is also enhanced, and the relaxation time is as low as 0.58 s. Furthermore, the supercapacitor shows an excellent cycling performance of 96.51 % retention after 4000 cycles. The remarkable results presented here illustrate that the redox strategy is a facile and straightforward approach to improve the performances of SWCNT electrodes.

Potassium-Based Dual-Ion Batteries Operating at -60 °C Enabled By Co-Intercalation Anode Chemistry.

Battery performance at subzero is restricted by sluggish interfacial kinetics. To resolve this issue, potassium-based dual-ion batteries (K-DIBs) based on the polytriphenylamine (PTPAn) cathode with anion storage chemistry and the hydrogen titanate (HTO) anode with K+ /solvent co-intercalation mechanism are constructed. Both the PTPAn cathode and the HTO anode do not undergo the desolvation process, which can effectively accelerate the interfacial kinetics at subzero. As revealed by theoretical calculations and experimental analysis, the strong K+ /solvent binding energy in the dilute electrolyte, the charge shielding effect of the crystal water, and the uniform SEI layer with high content of the flexible organic species synergically promote HTO to undergo K+ /solvent co-intercalation behavior. The special co-intercalation mechanism and anion storage chemistry enable HTO||PTPAn K-DIBs with superior rate performance and cycle durability, maintaining a capacity retention of 94.1% after 6000 cycles at -40 °C and 91% after 1000 cycles at -60 °C. These results provide a step forward for achieving high-performance energy storage devices at low temperatures.

Methyl 2-[2-(benzyl-oxycarbon-ylamino)-propan-2-yl]-5-hy-droxy-1-methyl-6-oxo-1,6-dihydro-pyrimidine-4-carboxyl-ate.

The title pyrimidine derivative, C(18)H(21)N(3)O(6), was obtained by the reaction of methyl 2-[2-(benzyl-oxycarbon-yl)amino-propan-2-yl]-5-hy-droxy-6-oxo-1,6-dihydro-pyrimidine-4-carboxyl-ate with dimethyl sulfate in dimethyl sulfoxide. The mol-ecule has a V-shaped structure, the phenyl and the pyrimidine rings making a dihedral angle of 43.1 (1)°. The methyl group substituting the pyrimidine ring deviates slightly from the ring mean-plane [C-N-C-C torsion angle = 5.49 (15)°], and the methyl ester substituent has a conformation suitable for the formation of an intra-molecular O-H⋯O hydrogen bond with the hydroxyl functionality. In the crystal, molecules are linked into chains along the b axis by N-H⋯O hydrogen bonds.

Tailoring Nitrogen Terminals on MXene Enables Fast Charging and Stable Cycling Na-Ion Batteries at Low Temperature.

Sodium-ion batteries stand a chance of enabling fast charging ability and long lifespan while operating at low temperature (low-T). However, sluggish kinetics and aggravated dendrites present two major challenges for anodes to achieve the goal at low-T. Herein, we propose an interlayer confined strategy for tailoring nitrogen terminals on Ti3C2 MXene (Ti3C2-Nfunct) to address these issues. The introduction of nitrogen terminals endows Ti3C2-Nfunct with large interlayer space and charge redistribution, improved conductivity and sufficient adsorption sites for Na+, which improves the possibility of Ti3C2 for accommodating more Na atoms, further enhancing the Na+ storage capability of Ti3C2. As revealed, Ti3C2-Nfunct not only possesses a lower Na-ion diffusion energy barrier and charge transfer activation energy, but also exhibits Na+-solvent co-intercalation behavior to circumvent a high de-solvation energy barrier at low-T. Besides, the solid electrolyte interface dominated by inorganic compounds is more beneficial for the Na+ transfer at the electrode/electrolyte interface. Compared with of the unmodified sample, Ti3C2-Nfunct exhibits a twofold capacity (201 mAh g-1), fast-charging ability (18 min at 80% capacity retention), and great superiority in cycle life (80.9%@5000 cycles) at - 25 °C. When coupling with Na3V2(PO4)2F3 cathode, the Ti3C2-Nfunct//NVPF exhibits high energy density and cycle stability at - 25 °C.