Polyvinylpyrrolidone regulated synthesis of mesoporous titanium niobium oxide as high-performance anode for lithium-ion batteries

Engineering of Cerium Modified TiNb2O7 Nanoparticles For Low-Temperature Lithium-Ion Battery

Although TiNb2O7 (TNO) with comparable operating potential and ideal theoretical capacity is considered to be the most ideal replacement for negative Li4Ti5O12 (LTO), the low ionic and electronic conductivity still limit its practical application as satisfactory anode for lithium-ion batteries (LIBs) with high-power density. Herein, TNO nanoparticles modified by Cerium (Ce) with outstanding electrochemical performance are synthesized. The successful introduction of Ce3+ in the lattice leads to increased interplanar spacing, refined grain size, more oxygen vacancy, and a smaller lithium diffusion barrier, which are conducive to improve conductivity of both Li+ and electrons. As a result, the modified TNO reaches high reversible capacity of 256.0 mA h g-1 at 100 mA g-1 after 100 cycles, and 183.0 mA h g-1 even under 3200 mA g-1. In particular, when the temperature drops to -20 °C, the cell undergoing 1500 cycles at a high current density of 500 mA g-1 can still reach 89.7 mA h g-1, corresponding to a capacity decay rate per cycle of only 0.033%. This work provides a new way to improve the electrochemical properties of alternative anodes for LIBs at extreme temperature.

Polyvinylpyrrolidone-assisted synthesis of ultrathin multi-nanolayered Cu2Nb34O87-x for advanced Li+ storage

The ultrathin multi-nanolayered structure with ultrathin monolayer thickness (<10 nm) and certain interlayer spacing can significantly shorten Li+ paths and alleviate the volume effect for Li+-storage materials. However, unlike layered materials such as MXene and MoS2, shear ReO3-type niobates have difficulty forming ultrathin multi-nanolayered structures due to their crystal structures, which still remains a challenge. Herein, by a polyvinylpyrrolidone (PVP)-assisted solvothermal method, we first synthesize ultrathin multi-nanolayered Cu2Nb34O87-x with oxygen vacancies composed of ultrathin nanolayers (2-10 nm in thickness) and interlayer spacing (1-5 nm). Oxygen vacancies can radically enhance the inherent electronic/ionic conductivity and Li+ diffusion coefficient of this material. The PVP-induced formation mechanism of this material is expounded in detail. The well-preserved ultrathin multi-nanolayered structure and excellent multi-electron electrochemical reversibility (Nb5+ ↔ Nb4+ ↔N b3+ and Cu2+ ↔ Cu+) of this material during cycling are fully verified. Based on an ultrathin multi-nanolayered structure and oxygen vacancies, this material as the anode of lithium-ion batteries is highly competitive among reported shear ReO3-type Cu-Nb-O anodes, displaying a high reversible capacity (315.3 mAh g-1 after 300 cycles at 1 C), durable cycling stability (85.7 % capacity retention after 1000 cycles at 10 C), and outstanding rate performance. Moreover, the application of this material to lithium-ion capacitors generates a large energy density (97.9 Wh kg-1 at 87.5 W kg-1) and a high power density (17,500 W kg-1 at 12.6 Wh kg-1), thus further indicating its fast faradaic pseudocapacitive behavior for practical applications. The results of this work indicate a breakthrough in synthesizing ultrathin multi-nanolayered shear ReO3-type niobates.

Rational design of hollow Ti2Nb10O29 nanospheres towards High-Performance pseudocapacitive Lithium-Ion storage

Ti2Nb10O29, as one of the most promising anode materials for lithium-ion batteries (LIBs), possesses excellent structural stability during lithiation/delithiation cycling and higher theoretical capacity. However, Ti2Nb10O29 faces some challenges, such as insufficient ion diffusion coefficient and poor electronic conductivity. To overcome these problems, this study investigates the effect of applying nanostructure engineering on Ti2Nb10O29 and the lithium storage behaviors. We successfully synthesized hollow Ti2Nb10O29 nanospheres (h-TNO NSs) via solvothermal method using phenolic resin nanospheres as the template. The effects of using a template or not and the annealing atmospheres on the microstructures of the as-prepared Ti2Nb10O29 are investigated. Different nanostructures (porous Ti2Nb10O29 nanoaggregates (p-TNO NAs) without a template and core-shelled Ti2Nb10O29@C nanospheres (cs-TNO@C NSs)) were formed through annealing in Ar. When examined as anodes for LIBs, the h-TNO NSs electrode with hollow spherical structure displayed a better lithium storage performance. Compared to its counterparts, p-TNO NAs and cs-TNO@C NSs, h-TNO NSs electrode exhibited a higher reversible capacity of 282.5 mAh g-1 at 1C, capacity retention of 79.5% (i.e., 224.6 mAh g-1) after 200 cycles, and a higher rate capacity of 173.1 mAh g-1 at 10C after 600 cycles. The excellent electrochemical performance of h-TNO NSs is attributed to the novel structure. The hollow nanospheres with cavities and thin shells not only exposed more active sites and improved ion diffusion, but also buffered the volume variation upon cycling and facilitated electrolyte penetration. This consequently enhanced the lithium storage performance of the electrode and its high pseudocapacitive contribution (90% at 1.0 mV s-1).

Surfactant regulated Core-Double-Shell NF@NiO nanosheets matrix as integrated anodes for Lithium-Ion batteries

The direct oxidation of three-dimensional nickel foam (3D NF) to nickel oxide (NiO) as integrated anode material for lithium-ion batteries (LIBs) has attracted significant attention towards achieving high-areal-capacity and high-energy density LIBs. However, the rate capability of such monolithic NiO in LIBs usually falls off rapidly due to the poor electrical conductivity that hindered its ionic transport kinetics. Herein, to ease the ionic transport constrains, a surfactant-regulated strategy is developed for preparing in-situ core-double-shell architecture that consists of core nickel skeleton, dense nickel oxide shell and porous nickel oxide nanosheets (NS) shell as anode materials for LIBs. Among the three employed surfactants including cationic surfactant, anionic surfactant and nonionic surfactant, the anionic surfactant (sodium dodecyl sulfate, SDS) modulated anode denoted SDS-NF@NiONS exhibits ultrahigh reversible areal capacity of 8.64 mAh cm-2@ 0.4 mA cm-2, and excellent rate areal capacity of 5.20 mAh cm-2 @ 3.0 mA cm-2, which did not only show the best ever reported NiO-based high-areal-capacity based electrodes, but also demonstrate impressive performance in practical full cell LIBs. In addition, in-situ Raman and kinetic analyses confirm the mechanism of Li-ion storage and facile ionic transport kinetics in this proposed design.

Bulk Modification of Porous TiNb2 O7 Microsphere to Achieve Superior Lithium-Storage Properties at Low Temperature

TiNb2 O7 , as a promising alternative of Li4 Ti5 O12 , exhibits giant potential as low-temperature anode due to its higher theoretical capacity and comparable structural stability. However, the sluggish electronic conductivity still remains a challenge. Herein, bulk modification of Cu+ doping in porous TiNb2 O7 microsphere is proposed via a simple one-step solvothermal method with subsequent calcination treatment. The results show that the electronic conductivity is improved effectively due to the reduced band gap after doping, while enhanced lithium-ion diffusion is achieved benefiting from the increased interplanar spacing. Therefore, the optimal sample of Cu0.06 Ti0.94 Nb2 O7 exhibits a high reversible capacity of 244.4 mA h g-1 at 100 mA g-1 after 100 cycles, superior rate capability, and long-term cycling stability at 1000 mA g-1 at room temperature. Particularly, it can also display good performance in a wide temperature range from 25 to -30 °C, including a reversible capacity of 76.6 mA h g-1 at -20 °C after 200 cycles at 200 mA g-1 . Moreover, Cu0.06 Ti0.94 Nb2 O7 //LiFePO4 full cell can deliver a high reversible capacity of 177.5 mA h g-1 at 100 mA g-1 . The excellent electrochemical properties at both ambient and low-temperatures demonstrate the great potential of Cu+ -doped TiNb2 O7 in energy-storage applications.

Theory-Driven Design of a Cationic Accelerator for High-Performance Electrolytic MnO2 -Zn Batteries

Aqueous electrolytic MnO₂ -Zn batteries are considered as one of the most promising energy-storage devices for their cost effectiveness, high output voltage, and safety, but their electrochemical performance is limited by the sluggish kinetics of cathodic MnO₂ /Mn²⁺ and anodic Zn/Zn²⁺ reactions. To overcome this critical challenge, herein, a cationic accelerator (CA) strategy is proposed based on the prediction of first-principles calculations. Poly(vinylpyrrolidone) is utilized as a model to testify the rational design of the CA strategy. It manifests that the CA effectively facilitates rapid cations migration in electrolyte and adequate charge transfer at electrode-electrolyte interface, benefiting the deposition/dissolution processes of both Mn²⁺ and Zn²⁺ cations to simultaneously improve kinetics of cathodic MnO₂ /Mn²⁺ and anodic Zn/Zn²⁺ reactions. The resulting MnO₂ -Zn battery regulated by CA exhibits large reversible capacities of 455 mAh g^-1 and 3.64 mAh cm^-2 at 20 C, as well as a long lifespan of 2000 cycles with energy density retention of 90%, achieving one of the best overall performances in the electrolytic MnO₂ -Zn batteries. This comprehensive work integrating theoretical prediction with experimental studies provides opportunities to the development of high-performance energy-storage devices.