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A series of Li 2 BaTi 6 O 14 samples are synthesized by a traditional solid-state method by calcining at different temperatures from 800 to 1000 °C. Structural analysis and electrochemical evaluation suggest that the optimum calcining temperature for Li 2 BaTi 6 O 14 is 950 °C. The Li 2 BaTi 6 O 14 calcined at 950 °C exhibits a high purity phase with an excellent reversible capacity of 145.7 mAh g −1 for the first cycle at a current density of 50 mA g −1 . After 50 cycles, the reversible capacity can be maintained at 137.7 mAh g −1 , with the capacity retention of 94.51%. Moreover, this sample also shows outstanding rate property with a high reversible capacity of 118 mAh g −1 at 300 mA g −1 . The excellent electrochemical performance is attributed to the stable lithium storage host structure, decreased electrochemical resistance and improved lithium-ion diffusion coefficient. In-situ and ex-situ structure analysis shows that the electrochemical reaction of Li 2 BaTi 6 O 14 with Li is a highly reversible lithiation–delithiation process. Therefore, Li 2 BaTi 6 O 14 may be a promising alternative anode material for lithium-ion batteries.

Using carbon nanotube (CNT) as conductive additive, (NH 4 ) 2 Ce(NO 3 ) 5 ·4H 2 O/CNT is prepared from (NH 4 ) 2 Ce(NO 3 ) 6 by a facile solution method and used as high capacity anode material for the first time. Morphology and structure investigation shows that (NH 4 ) 2 Ce(NO 3 ) 5 ·4H 2 O/CNT exhibits high purity phase with particle size of 0.1–1.0 μm. In the composite, CNT provides a three-dimensional conductive network for electron transportation and can maintain the whole structure upon electrochemical cycles. For comparison, (NH 4 ) 2 Ce(NO 3 ) 5 ·4H 2 O and (NH 4 ) 2 Ce(NO 3 ) 5 ·4H 2 O/carbon black ((NH 4 ) 2 Ce(NO 3 ) 5 ·4H 2 O/CB) are also prepared by the same method. Impurity phase of (NH 4 ) 3 Ce 2 (NO 3 ) 9 can be detected in both (NH 4 ) 2 Ce(NO 3 ) 5 ·4H 2 O and (NH 4 ) 2 Ce(NO 3 ) 5 ·4H 2 O/CB. Electrochemical testing results reveals that (NH 4 ) 2 Ce(NO 3 ) 5 ·4H 2 O/CNT shows lower initial discharge capacity (1683.6 mAh g −1 ) than (NH 4 ) 2 Ce(NO 3 ) 5 ·4H 2 O (1972.8 mAh g −1 ) in the first cycle. However, (NH 4 ) 2 Ce(NO 3 ) 5 ·4H 2 O/CNT shows the highest reversible capacity among all the three samples. After 30 cycles, it can deliver a reversible capacity of 818.5 mAh g −1 , which is much higher than that of (NH 4 ) 2 Ce(NO 3 ) 5 ·4H 2 O (50.6 mAh g −1 ) and (NH 4 ) 2 Ce(NO 3 ) 5 ·4H 2 O/CB (208.8 mAh g −1 ). It suggests that the enhanced electrochemical properties are attributed to the introduction of CNT, which improves the electronic conductivity and structural stability during repeated cycles.

A series of Na x Li 4−x Ti 6 O 14 (0 ≤ x ≤ 4) are prepared by solid-state method and their structures, morphologies and electrochemical properties are compared by changing the Na/Li atomic ratio. It can be found that two single-phase samples of Na 2 Li 2 Ti 6 O 14 and Na 4 Ti 6 O 14 and three multi-phase samples of Li 4 Ti 6 O 14 (Li 4 Ti 5 O 12 /TiO 2 ), NaLi 3 Ti 6 O 14 (Na 2 Li 2 Ti 6 O 14 /Li 4 Ti 5 O 12 /TiO 2 ) and Na 3 LiTi 6 O 14 (Na 2 Li 2 Ti 6 O 14 /Na 2 Ti 3 O 7 ) can be formed by using a stoichiometric ratio of starting materials based on the formula of Na x Li 4−x Ti 6 O 14 . Besides, different Na/Li atomic ratios in Na x Li 4−x Ti 6 O 14 also induce the morphology evolution shifting from round-shape to polyhedron-shape, and then to square-shape with the increase of Na content. Electrochemical tests show that Li 4 Ti 6 O 14 delivers the highest charge capacities of 116 mAh g −1 at 100 mA g −1 , 91.5 mAh g −1 at 200 mA g −1 , 77.5 mAh g −1 at 300 mA g −1 and 66.9 mAh g −1 at 400 mA g −1 among five samples. For comparison, Na 4 Ti 6 O 14 only reveals the reversible capacities of 38.6 mAh g −1 at 100 mA g −1 , 30.2 mAh g −1 at 200 mA g −1 , 24.8 mAh g −1 at 300 mA g −1 and 20.9 mAh g −1 at 400 mA g −1 . It suggests that Li 4 Ti 6 O 14 is the most potential lithium storage material among all the Na x Li 4−x Ti 6 O 14 samples.

To improve the electrochemical performance of Na 2 Li 2 Ti 6 O 14 , carbon black (CB), graphene (GN) and carbon nanotube (CNT) are introduced to fabricate high conductive Na 2 Li 2 Ti 6 O 14 /CB, Na 2 Li 2 Ti 6 O 14 /GN, Na 2 Li 2 Ti 6 O 14 /CNT and Na 2 Li 2 Ti 6 O 14 /CB/GN/CNT by a solid state method. It can be found that only CNT forms a complete three-dimensional conductive network which embeds the randomly distributed Na 2 Li 2 Ti 6 O 14 particles, leading to an improvement of electronic conductivity. The results of cyclic voltammetry, electrochemical impedance spectroscopy and charge–discharge tests reveal that Na 2 Li 2 Ti 6 O 14 /CNT obtains the lowest redox polarization and the highest peak current among all the five samples. As a result, Na 2 Li 2 Ti 6 O 14 /CNT shows the best cycling and rate performances among all the five samples. It reveals a charge capacity of 111.4 mAh g −1 at 100 mA g −1 , 110 mAh g −1 at 200 mA g −1 , 103.9 mAh g −1 at 300 mA g −1 and 98.9 mAh g −1 at 400 mA g −1 . For comparison, bare Na 2 Li 2 Ti 6 O 14 only displays a charge capacity of 89.9 mAh g −1 at 100 mA g −1 , 79.7 mAh g −1 at 200 mA g −1 , 73.7 mAh g −1 at 300 mA g −1 and 69.4 mAh g −1 at 400 mA g −1 . It indicates that the introduction of CNT is more effective to improve the performance of Na 2 Li 2 Ti 6 O 14 than CB, GN and CB/GN/CNT.

[Bi6O4](OH)4(NO3)6·4H2O, [Bi6O4](OH)4(NO3)6·H2O and [Bi6O4](OH)4(NO3)6·H2O/C, derivated from Bi(NO3)3·5H2O, are firstly investigated for the electrochemical activity as anode materials for lithium-ion batteries. Electrochemical results show that [Bi6O4](OH)4(NO3)6·4H2O can deliver a higher initial discharge specific capacity (2792.9 mAh g−1) than that of [Bi6O4](OH)4(NO3)6·H2O (832.2 mAh g−1) and [Bi6O4](OH)4(NO3)6·H2O/C (1169.3 mAh g−1). However, the capacity retention (60.3%) and reversible specific capacity (365.5 mAh g−1) of [Bi6O4](OH)4(NO3)6·H2O/C are much higher than those of [Bi6O4](OH)4(NO3)6·H2O (4.75% and 39.6 mAh g−1) and [Bi6O4](OH)4(NO3)6·4H2O (15.9% and 289.4 mAh g−1) in the first 30 cycles. The improved electrochemical properties are attributed to the decrease of crystal water in the structure and the introduction of carbon black as conductive additive and volume change buffer. The reaction mechanism of [Bi6O4](OH)4(NO3)6·H2O/C with Li is also studied in detail by using various ex-situ and in-situ techniques during the initial charge-discharge cycle. It can be found that the electrochemical reaction of [Bi6O4](OH)4(NO3)6·H2O with Li leads to the preliminary formation of metal Bi, LiNO3, LiOH, Li2O and H2O and then the alloying reaction to form Li–Bi alloys.

For the first time, Cu(NO3)2·xH2O (x ≤ 2.5) is investigated as a new lithium storage anode material for lithium-ion batteries. The impressive characteristic of Cu(NO3)2·xH2O(x ≤ 2.5)/Li cell is the high initial discharge capacity reaching to around 2200 mAh g−1. To make a comparison, Cu(NO3)2·2.5H2O electrodes are used as raw materials and heat-treated at 80, 120 and 160 °C. Among all the three samples, Cu(NO3)2·xH2O (x

In this paper, a series of LiVPO 4 F-based samples are prepared through sintering LiVPO 4 F at different temperatures under air. Experimental results show that the pristine sample is oxidized to a new compound Li 1 − x VPO 4 F 1 − y O z (0 x y ≤ 1, 0.9 z ≤1) with similar structure of LiVPO 4 O under air at 550 °C or higher one. In - situ X-ray diffraction patterns indicate that the original material LiVPO 4 F undergoes two two-phase structural evolutions upon Li + electrochemical extraction at average operating potentials at 4.26 and 4.30 V, corresponding to the continuous transformation of LiVPO 4 F → Li 0.72 VPO 4 F → VPO 4 F in the first charge process. In the reverse discharge process, there is only one two-phase structural transition VPO 4 F → LiVPO 4 F without the appearance of the intermediate phase Li 0.72 VPO 4 F on Li + insertion reaction at 4.18 V. Therefore, the extraction/insertion process of LiVPO 4 F is an asymmetrical phase transformation. When the sintering temperature is raised to 550 °C, Li 1− x VPO 4 F 1− y O z exhibits extremely poor electrochemical performance, which is attributed to the volatilization loss of lithium and the replacement of fluorine by oxygen in the structure during the sintering process under air. However, Li 1 − x VPO 4 F 1 − y O z has a very stable structure during the whole process of galvanostatic charge/discharge cycles as confirmed by in - situ X-ray diffraction technique.

Spherical LiNi 0.5 Co 0.3 Mn 0.2 O 2 samples with the particle size distribution between 10 and 20 μm are prepared by a hydroxide co-precipitation method and subsequent high temperature solid state calcination. Electrochemical results show that the reversible lithium storage capacities of spherical LiNi 0.5 Co 0.3 Mn 0.2 O 2 cathode after 20 cycles are 121.5, 154.2 and 99.3 mAh g −1 in 2.0–4.3 V, 2.0–4.6 V and 2.0–4.9 V, respectively. The structural evolutions of layered materials in different working potential ranges are carefully studied by homemade in-situ X-ray diffraction techniques. It is found that the formation of hexagonal phase H3 is the main source resulting in poor electrochemical properties, where the hexagonal phase H2 to hexagonal phase H3 transition occurs at about 4.7 V in the charge process. As a result, it is expected that the suppression of hexagonal phase H3 can achieve a long-term cyclability and high reversible capacity for LiNi 0.5 Co 0.3 Mn 0.2 O 2 . Therefore, spherical LiNi 0.5 Co 0.3 Mn 0.2 O 2 cathode shows the highest reversible lithium storage capacity of 154.2 mAh g −1 in 2.0–4.6 V after 20 cycles among all the three electrochemical working windows.