•Li2Na2Ti6O14 is prepared by a solid state reaction.•Cu/C layer is coated on Li2Na2Ti6O14 by a thermal decomposition.•Cu/C coating layer improves the electrochemical properties of Li2Na2Ti6O14.•Core–shell Li2Na2Ti6O14@Cu/C shows a reversible capacity of 120.3 mAh g−1.Core–shell Li2Na2Ti6O14@Cu/C is prepared by a preliminary formation of Li2Na2Ti6O14 by solid state reaction and a following coating process with Cu/C layer by thermal decomposition. The amorphous Cu/C coating layer reveals a thickness of 5 nm on the surface of Li2Na2Ti6O14, which improves the electronic conductivity and charge transfer rate of active materials. As a result, Li2Na2Ti6O14@Cu/C shows lower electrochemical polarization and quicker kinetic behavior compared to bare Li2Na2Ti6O14. Cycled at 50 mA g−1, Li2Na2Ti6O14@Cu/C can deliver a reversible capacity of 120.3 mAh g−1 after 50 cycles, which is much higher than the value of 96.8 mAh g−1 obtained by Li2Na2Ti6O14. Even kept at 400 mA g−1, a reversible lithium storage capacity of 76.3 mAh g−1 can be delivered by Li2Na2Ti6O14@Cu/C. The improved electrochemical properties of Li2Na2Ti6O14 are attributed to the electronic conductive Cu/C coating layer on the surface.

•For the first time, Cu(NO3)2·xH2O is studied as a novel lithium storage anode material.•Cu(NO3)2·xH2O exhibits an initial discharge capacity of about 2200 mAh g−1.•Cu(NO3)2·xH2O obtained at 160 °C delivers a reversible capacity of 597.6 mAh g−1 after 30 cycles.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 < 2.5) obtained at 160 °C shows the highest reversible capacity of 597.6 mAh g−1 and the best cycling stability after 30 cycles. The difference in electrochemical behaviors is attributed to the variation of surface morphology, crystal water and particles size after heat-treatment at different temperatures. Besides, the thermal reaction results also show that Cu(NO3)2·xH2O (x < 2.5) obtained at 160 °C has the highest thermal stability among all the three samples after repeated cycles. The present findings can provide the fact that Cu(NO3)2·xH2O (≤2.5) may be a promising anode material for lithium-ion batteries.

•Li4Ti5O12@C is prepared by a facile carbon coating strategy.•Amorphous carbon coating layer shows a thickness of 4–6 nm.•Li4Ti5O12@C delivers a capacity of 160.6 mA h g−1 at 20 mA g−1 in 1.0–2.0 V.•Li4Ti5O12@C displays a capacity of 205.1 mA h g−1 at 1500 mA g−1 in 0.0–2.0 V.In this study, carbon-encapsulated Li4Ti5O12 particles are prepared by a facile carbon formation strategy. Under the thermal hydrolysis of acetate in Ar atmosphere, Li4Ti5O12 particles are uniformly coated by amorphous carbon layer with the thickness of 4–6 nm. The electrochemical properties of Li4Ti5O12@C are characterized as high rate anode material for lithium ion batteries. Electrochemical results show that Li4Ti5O12@C can respectively deliver the reversible lithium storage capacities of 155.0, 134.7 and 60.3 mA h g−1 at 20, 600 and 1500 mA g−1 in a narrow working window of 1.0–2.0 V. Cycled in a broad potential range of 0.5–2.0 V, Li4Ti5O12@C remains the reversible charge capacities of 158.2, 134.5 and 114.7 mA h g−1 at 20, 600 and 1500 mA g−1 with capacity retentions of 91.5%, 97.5% and 100%, respectively. Even working between 0.0 and 2.0 V, Li4Ti5O12@C can still display outstanding electrochemical properties with the reversible capacities of 220.2, 200.6 and 205.1 mA h g−1 at 20, 600 and 1500 mA g−1.

•In situ growth of CNTs on LiFePO4 is prepared by hydrolysis of acetylene.•The existence of P element in catalysts results in the formation of coiled CNTs.•Crosslinked CNTs provide electronic conductive pathways.•LiFePO4@CNTs shows a reversible capacity of 108.0 mA h g−1 at 10 C.In this paper, LiFePO4@CNTs is fabricated by in situ growth of CNTs on the surface of LiFePO4 particles. The use of Ni–P alloy as catalyst results in the formation of coiled CNTs. The crosslinked CNTs provide good electronic conductive pathways interconnecting LiFePO4 particles. By using as cathode material for lithium ion battery, LiFePO4@CNTs shows higher electronic conductivity and charge transfer rate than those of the pristine LiFePO4 before coating. As a result, LiFePO4@CNTs displays outstanding lithium storage capacity and rate property. Electrochemical results reveal that LiFePO4@CNTs can deliver the reversible capacities of 161.3 mA h g−1 at 0.2 C and 108.0 mA h g−1 at 10 C. For comparison, bare LiFePO4 only reveals reversible capacities of 144.1 mA h g−1 at 0.2 C and 90.9 mA h g−1 at 10 C.Graphical abstract

•PbSbO2Cl and PbCl2/Sb4O5Cl2 are prepared by a solution method.•PbCl2/Sb4O5Cl2 shows higher lithium storage capacity than PbSbO2Cl.•PbCl2/Sb4O5Cl2 shows better cycling stability than PbSbO2Cl.•PbCl2/Sb4O5Cl2 shows a reversible capacity of 339.7 mA h g−1 after 30 cycles.In this work, PbCl2/Sb4O5Cl2 and PbSbO2Cl are prepared by a simple solution route, and compared by using as lithium storage materials. PbCl2/Sb4O5Cl2 is the intermediate precursor for hydrothermal preparing PbSbO2Cl. Morphology analysis shows that PbCl2/Sb4O5Cl2 is composed of irregular particles in the range of 50–100 nm and PbSbO2Cl consists of well-dispersed bulks with the particle size of 200–500 nm. Similar chemical composition between PbCl2/Sb4O5Cl2 and PbSbO2Cl make they show similar electrochemical behaviors. However, different morphology and structure also make PbCl2/Sb4O5Cl2 and PbSbO2Cl exhibit different lithium storage capacity and cycling performance. Charge/discharge tests reveal that nanocomposite PbCl2/Sb4O5Cl2 can deliver a higher initial lithiation capacity (1036.7 mA h g−1) than PbSbO2Cl (993.8 mA h g−1). Upon repeated cycles, PbCl2/Sb4O5Cl2 also shows better electrochemical properties than PbSbO2Cl, which may be contributed to the maintaining of structural stability by nanocomposite structure. As a result, PbCl2/Sb4O5Cl2 delivers a reversible capacity of 339.7 mA h g−1 after 30 cycles.

In this paper, we reported on a comparison of LiVPO4F to Li4Ti5O12 as anode materials for lithium-ion batteries. Combined with powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, galvanostatic discharge/charge tests and in situ X-ray diffraction technologies, we explore and compare the insertion/extraction mechanisms of LiVPO4F based on the V3+/V2+/V+ redox couples and Li4Ti5O12 based on the Ti4+/Ti3+ redox couple cycled in 1.0–3.0 V and 0.0–3.0 V. The electrochemical results indicate that both LiVPO4F and Li4Ti5O12 are solid electrolyte interphase free materials in 1.0–3.0 V. The insertion/extraction mechanisms of LiVPO4F and Li4Ti5O12 are similar with each other in 1.0–3.0 V as proved by in situ X-ray diffraction. It also demonstrates that both samples possess stable structure in 0.0–3.0 V. Additionally, the electrochemical performance tests of LiVPO4F and Li4Ti5O12 indicate that both samples cycled in 0.0–3.0 V exhibit much higher capacities than those cycled in 1.0–3.0 V but display worse cycle performance. The rate performance of Li4Ti5O12 far exceeds that of LiVPO4F in the same electrochemical potential window. In particular, the capacity retention of Li4Ti5O12 cycled in 1.0–3.0 V is as high as 98.2% after 20 cycles. By contrast, Li4Ti5O12 is expected to be a candidate anode material considering its high working potential, structural zero-strain property, and excellent cycle stability and rate performance.Keywords: in situ X-ray diffraction; anode materials; Li4Ti5O12; lithium-ion batteries; LiVPO4F;

We report the development of PbSbO2Cl as a new anode material for lithium-ion batteries. It is prepared by a simple hydrothermal method from Pb(NO3)2 and SbCl3. The as-prepared PbSbO2Cl shows a well-dispersed nano-micro structure with particle sizes of 200–500 nm. The initial discharge capacity of PbSbO2Cl is 1011.0 mAh g−1 corresponding to 14.6 Li per formula storage in the structure. In the inverse charge process, a reversible capacity of 731.8 mAh g−1 can be delivered. This suggests that PbSbO2Cl may be a promising high-capacity anode material for lithium-ion batteries.

Li1.15V3O8 nanobelts with length 3 μm, width 200 nm and 20–50 nm in thickness are prepared on a large scale by a tartaric acid-assisted sol–gel technique. They show greater reversibility of the lithium ion insertion/extraction reaction than those synthesized without the addition of tartaric acid. After twenty cycles, the reversible lithium storage capacities of Li1.15V3O8 prepared from tartaric acid assisted and free techniques are 231.0 and 194.5 mAh/g at a current density of 30 mA g−1, respectively. Cycled at 20 mA g−1 in 1.5–4.1 V, Li1.15V3O8 nanobelts can deliver discharge and charge capacities of 297.0 and 298.4 mAh/g, respectively. Increasing the charge/discharge current density to 2400 mA g−1, the lithiation and delithiation capacities of Li1.15V3O8 nanobelts can be mantianed at 184.2 and 184.2 mAh/g, respectively. In situXRD observation reveals that the host structure of Li1.15V3O8 nanobelts will not be destroyed with a discharge process to 0.0 V at 20 mA g−1 or a short circuit for 24 h. Over-lithiation can induce the formation of an inactive compound, leading to poor electrochemical properties of Li1.15V3O8 nanobelts. The first lithiation/delithiation process in 0.0–4.1 V or 1.5–4.1 V is a reversible reaction at a current density of 60 mA g−1, and is composed of reversible single-phase structural evolutions in a high voltage region and two-phase structural transitions in a low voltage region. The electrochemical properties of Li1.15V3O8 nanobelts are poorer at the 10th cycle in 0.0–4.1 V than that obtained in 1.5–4.1 V. In situXRD results indicate that the breakdown of two-phase transition in a low voltage region is the main factor for poor cycleability. Besides, a delay of structural evolution and asymmetry lithiation/delithiation process can be observed at high rates, which may also be responsible for the deterioration of cycleability of Li1.15V3O8 nanobelts.

In this paper, Li4Ti5O12@CNT composites are fabricated by a controlled in situ growth of CNTs on the surface of Li4Ti5O12. The formation of coiled CNTs occurs by the electroless loading of Ni–P catalysts on the surface of Li4Ti5O12. Coiled CNTs provide electron bridges interconnecting the Li4Ti5O12 particles to form a nano/micro-structured conductive hyper-network. The electronic conductivity of Li4Ti5O12@CNT composites is better than that of the sample before coating. As a result, Li4Ti5O12@CNT composites show superior lithium storage properties comparable to the pristine Li4Ti5O12. Based on electrochemical analysis, it is obvious that Li4Ti5O12@CNT composites can deliver reversible charge capacities of 149.2, 102.6, 73.3 and 47.5 mA h g−1 at 0.2 C, 10 C, 20 C and 50 C, respectively.

In this paper, we describe the preparation and dual-use of carbon nanofibers/Si (CNFs/Si) composites as the source/drain contacts for copper phthalocyanine (CuPc) based thin film transistors (TFTs) and as anode materials for high performance lithium-ion batteries. The CNFs/Si composites are prepared by a facile chemical vapor deposition (CVD) technique with iron nitrate as the catalyst source and acetylene as the carbon source. In the CNFs/Si structure, Si particles are tightly wrapped by CNFs with an average diameter of 15–30 nm and length of 1–2 μm. It can be seen that the catalysts are grown on the top tip of the CNFs. Based on the superior properties of the CNFs coating, the CNFs/Si composites are applied in different fields. Compared with CuPc based OTFTs with Au contacts, the performances of organic thin film transistors (OTFTs) with CNFs/Si contacts are significantly improved. For OTFTs with CNFs/Si contacts, they show the on-state current increasing from 9 × 10−9 to 3 × 10−7 A at the gate voltage of −40 V, field effect mobility increasing from 1.9 × 10−4 to 4.2 × 10−3 cm2 V−1 s−1, and threshold voltage shifting from 15 to 30 V for the saturation regime. These are attributed to the more effective charge-carrier injection of CNFs/Si contacts than of Au contacts. Besides, the CNFs/Si composites are also promising lithium storage host materials. They show excellent rate capability as anode materials for lithium batteries. The initial discharge and charge capacities of CNFs/Si composites at 0.05 C are 1491.6 and 1168.7 mAh g−1, respectively. For comparison, the initial discharge and charge capacities of the CNFs/Si composites at 0.60 C are 1197.8 and 941.4 mAh g−1, respectively. After twenty cycles, the discharge and charge capacities at 0.60 C are 834.4 and 733.9 mAh g−1, respectively.

In this paper, silica coated carbon sphere composites were synthesized by a facile hydrothermal method. During the preparation, carbon@silica composites were formed by hydrolysis and deposition of TEOS on the surface of carbon spheres. XRD patterns show that this coating layer is composed of crystallized SiO2. When different amounts of TEOS were added, carbon@silica composites show different surface morphologies formed by silica nucleation and growth, spreading into a thinly coated layer, repeatedly. These varied silica coating layers have a great effect on the SEI film formation and electrochemical properties of the carbon@silica composites. The surface morphology and onset formation voltage of the surface film are greatly dependent on the surface morphology and structure of carbon@silica composites. Similarly, the lithiation and delithiation behaviors are obviously affected by this silica coating layer. Carbon@silica composites can deliver a reversible capacity of 351 mAh·g−1 in 0.0–3.0 V after 30 cycles, which is higher than that of the pristine carbon spheres. The extra capacity mainly comes from the Li-storage in the micropores and disordered graphene layers after silica coating. By broadening the electrochemical cycling window, a higher reversible capacity of 511 mAh·g−1 can be delivered in the voltage range between −15 mV and 3.0 V. The excess capacity in the low voltage region is mainly associated with additional Li-storage in micropores. It indicates that carbon@silica composites are promising anode materials for lithium-ion batteries.

A series of LiNi0.5Co0.5−xTixO2 (0 ⩽ x ⩽ 0.5) are prepared by a tartaric acid-assisted sol–gel technique. The phase formation process is observed by TG–DTA. It is found that the target product appears at a temperature higher than 400 °C and completes to phase formation at 700 °C. The crystal structure and morphology are characterized by XRD, SEM and Raman spectroscopy. XRD patterns show that the as-prepared sample transforms from hexagonal structure into cubic structure with the increase of Ti content in LiNi0.5Co0.5−xTixO2. Raman spectra also demonstrate the successive substitution of Ti for Co in the structure with band blue-shift phenomenon. SEM images confirm that the as-prepared sample exhibits narrow and regular particles with the size between 0.5 and 1.5 μm. The apparent particle size of sample starts to decrease with x ⩽ 0.1, and the gradually increases by introducing Ti dopant with higher content (x ⩾ 0.15). The electrochemical behavior of the sample displays different characteristics after Ti substitution. It is found that the initial working potential increases with the increase of Ti doping content. As a result, the initial lithium storage capacity for trace Ti-doped sample is higher than that delivered by the pristine one. The decrease of reversible capacity for high degree Ti-doped sample is ascribed to the electrochemical inactivity of the cubic compound in the sample. Therefore, trace Ti doping is beneficial to achieve promising cathode material for lithium-ion batteries.Graphical abstractHighlights► A series of LiNi0.5Co0.5−xTixO2 (0 ⩽ x ⩽ 0.5) are prepared by a tartaric acid-assisted sol–gel technique. ► The structural evolution and electrochemical properties of LiNi0.5Co0.5−xTixO2 are determined by the Ti doping content. ► Trace Ti doping is beneficial to achieve promising Ni-based layered cathode material for lithium-ion batteries.

The surface physical and chemical behaviors of conductive additive acetylene black (AB) are studied after the samples are cycled at different working temperatures (−20, 20, and 60 °C). Working at low temperature (−20 °C), AB shows high polarization and poor electrochemical property. In addition, plenty of inorganic compounds are formed on the surface of AB. For comparison, the surface film on AB after being worked at 60 °C is comprised of an outer organic layer and an inner inorganic layer. Moreover, it consumes large electrical energy and results in irreversible trapped lithium for surface film formation. Furthermore, much more organic components can induce lower thermal stability of conductive additive. During repeated electrochemical cycles, the surface structure of AB experiences a series of changes of surface electrolyte decomposition products. It is found that the organic polymer in outer layer will decompose into other stable species, and partial surface fluorides in the inner layer will transform into other fluorides. The working temperature has a great effect on the final transformation products.

The electrochemical behaviors and lithium-storage mechanism of LiCoO2 in a broad voltage window (1.0−4.3 V) are studied by charge−discharge cycling, XRD, XPS, Raman, and HRTEM. It is found that the reduction mechanism of LiCoO2 with lithium is associated with the irreversible formation of metastable phase Li1+xCoII IIIO2−y and then the final products of Li2O and Co metal. During the charging process, the Li2O/Co mixture can be oxidized into CoO, and then the Li2O/CoO mixture can result in the formation of Co3O4 in the higher-voltage region. LixCoOy is the final product when the active material is charged to 4.3 V. During the subsequent cycles, the lithium uptake/release reactions are related to the reversible conversion of Co ↔ CoO ↔ Co3O4 ↔ LixCoOy.

Li1.15V3O8 nanobelts with length 3 μm, width 200 nm and 20–50 nm in thickness are prepared on a large scale by a tartaric acid-assisted sol–gel technique. They show greater reversibility of the lithium ion insertion/extraction reaction than those synthesized without the addition of tartaric acid. After twenty cycles, the reversible lithium storage capacities of Li1.15V3O8 prepared from tartaric acid assisted and free techniques are 231.0 and 194.5 mAh/g at a current density of 30 mA g−1, respectively. Cycled at 20 mA g−1 in 1.5–4.1 V, Li1.15V3O8 nanobelts can deliver discharge and charge capacities of 297.0 and 298.4 mAh/g, respectively. Increasing the charge/discharge current density to 2400 mA g−1, the lithiation and delithiation capacities of Li1.15V3O8 nanobelts can be mantianed at 184.2 and 184.2 mAh/g, respectively. In situXRD observation reveals that the host structure of Li1.15V3O8 nanobelts will not be destroyed with a discharge process to 0.0 V at 20 mA g−1 or a short circuit for 24 h. Over-lithiation can induce the formation of an inactive compound, leading to poor electrochemical properties of Li1.15V3O8 nanobelts. The first lithiation/delithiation process in 0.0–4.1 V or 1.5–4.1 V is a reversible reaction at a current density of 60 mA g−1, and is composed of reversible single-phase structural evolutions in a high voltage region and two-phase structural transitions in a low voltage region. The electrochemical properties of Li1.15V3O8 nanobelts are poorer at the 10th cycle in 0.0–4.1 V than that obtained in 1.5–4.1 V. In situXRD results indicate that the breakdown of two-phase transition in a low voltage region is the main factor for poor cycleability. Besides, a delay of structural evolution and asymmetry lithiation/delithiation process can be observed at high rates, which may also be responsible for the deterioration of cycleability of Li1.15V3O8 nanobelts.