We report here the electrochemical properties of Na₂Ti₃O₇, a potential non-carbon based, low-voltage anode material for room temperature sodium ion battery applications. A solid-state route was used to prepare Na₂Ti₃O₇. Further, XRD, SEM, TEM, HRTEM, SAED, XPS and EDX techniques were used to characterize the material. The Na/Na₂Ti₃O₇ cell displayed a charge capacity of 177 mA h g⁻¹ at 0.1 C rate. High rate and long term cyclic performance at different rates showed relatively stable storage capacities. Surprisingly, if the lower cut-off voltage is altered, the appearance of a new charge plateau is seen, with no apparent change in the discharge behaviour. The kinetics of sodium insertion and extraction are discussed utilizing CV and EIS techniques. We also report the sodium chemical diffusion coefficient of the Na₂Ti₃O₇/CB electrode estimated using GITT.

Lithium iron phosphate, LiFePO₄ (LFP), is considered to be a potential cathode material for lithium-ion batteries but its rate performance is significantly restricted by sluggish kinetics of electrons and lithium ions. A simple solvothermal method has been described in this article to synthesize carbon coated LFP (LFP/C) nanoplates with varying thickness from 20 to 500 nm by using different iron precursors. The influence of solvents on the morphology of the LFP in the solvothermal synthesis is also investigated. A uniform carbon coverage at the surfaces has been achieved by a selective chelating carbonising source, D-gluconic acid lactone. The smallest dimension of the nanoplates has been found to be the b-axis where the Li⁺ ion diffuses quickly. The overall capacity and rate performance have, in general, been found to increase with the decrease of thickness of the nanoplates. Hierarchical LFP/C with ∼30 nm thickness shows the best electrochemical performance of 167 mA h g⁻¹, followed by spindle (<20 nm thickness but aggregated, 121 mA h g⁻¹), plates (200–300 nm thickness, 110 mA h g⁻¹) and diamond shaped LFP/C (300–500 nm thickness, 82 mA h g⁻¹) at a current rate of 17mA g⁻¹ (0.1C rate). The spindle shaped LFP/C shows unexpected electrochemical performance since the nanoplates are heavily agglomerated in the bulk which prevents access for the liquid electrolyte, as well as additive Super P carbon, between neighbouring nanoplates during the fabrication of the composite electrodes. Hence, only the peripheral plates of the spindle are actively involved in the insertion/extraction of Li⁺ , while the core of the spindle shaped LFP/C is almost inactive, resulting in moderate storage behaviour.

Micrometre-sized mesoporous materials have characteristic grains as well as pores nearly in the same scale. Electrodes of mesoporous materials for lithium batteries have short transport lengths for Li⁺ ions due to their nano-sized grains (10–20 nm), and easy access for electrolytes due to their nanopores (5–10 nm). Such mesoporous materials have high packing densities unlike nanopowders, nanowires, nanorods and nanotubes. Despite such advantages, electronic conduction over micrometre-sized particles limits the rate performance of mesporous materials. Occasionally counductive thin layers (2–5 nm) of carbon or RuO₂ have been used to overcome such kinetic limitations and to achieve high storage performances. In this manuscript, we present a simple approach for the synthesis of mesoporous TiO₂ anatase using a soft-template method, which shows superior storage performance without such conductive surface layers. Various cationic surfactants with different chain lengths have been selected for this investigation to assist the formation of the mesoporous TiO₂ structure. Among these, cetyl trimethylammoniumbromide templated C16-TiO₂ has the highest surface area of 135 m² g⁻¹ and reversible capacity of 288, 220, 138,134 and 107 mAh g⁻¹ at 0.2, 1, 5, 10 and 30C respectively. The storage performance of the as-synthesized mesoporous TiO₂ is nearly five times better than the commercially available TiO₂ nanopowder. The packing density of meso-TiO₂ is found to be 6.6 times higher than the TiO₂ nanopowder. In addition, battery testing using mesoporous TiO₂ electrodes without the 15% carbon additive exhibits nearly the same performance at low rate as the meso-TiO₂ with carbon additives. These exciting results suggest a facile conduction path for electrons, a unique character of micrometre-sized mesoporous TiO₂ with highly interconnected nanograins of 15–20 nm.

The morphology of electrode materials is addressed as a key factor controlling rapid lithium storage in anisotropic systems such as LiFePO₄. In view of this, we have synthesized nanoplates of LiFePO₄ with a uniform coating of a 5 nm thick amorphous carbon layer by the solvothermal method and investigated their electrochemical storage behavior. The obtained nanoplates are well characterized by XRPD, SEM, HRTEM and XPS techniques. The thickness along the b-axis is found to be 30–40 nm; such a morphology favors short diffusion lengths for Li⁺ ions, while the external conductive carbon coating provides connectivity for facile electron diffusion, resulting in high rate performances. Increase in the size of the nanoplates results in poor lithium storage performance. The storage performance of nanoplates is compared with that of mesoporous nanoparticles of LiFePO₄ with non-uniform carbon coating. This paper thus describes the advantages of thinner nanoplates for high rate storage performances of battery electrode materials.

In this manuscript, a systematic investigation on the electrochemical performance of as-synthesized metal organic framework (MOF) Zn₃(HCOO)₆ with diamondoid structure for the Li storage using conversion reaction at low potential is described. Nearly an invariable capacity of 560 mAh g⁻¹ (9.6 moles of Li) was obtained up to 60 cycles at 60 mA g⁻¹ within the voltage range 0.005–3.0 V. The regeneration of the MOF during the cycling and the improved cyclability are evidenced from the electrochemical results along with ex situ PXRD, FTIR and TEM studies. The electrochemical cycling suggests that metal formate frameworks react reversibly with Li through conversion reaction. The matrix involved during the cycling was lithium formate rather than the typical Li₂O and this is well supported by the ex situ FTIR results. The thermodynamic feasibility to transform the lithium formate to transition metal formate is more highly favored than from Li₂O and this is further confirmed by reacting lithium formate with respective transition metal nitrates. The reversible formation or regeneration of FOR1 MOF plays a vital role in attaining the superior Li storage performance. Ultimately, the observation of improved storage performance and good cycling stability of Co₃(HCOO)₆ and Zn_1.5Co_1.5(HCOO)₆ , and the overall simple and eco-friendly synthesis method demonstrates that robust, thermally stable MOFs are a prospective class of electrode materials for Li ion batteries (LIBs).