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Although hard carbon is deemed to be the most potential industrialized sodium-ion batteries anode material, there are still some problems need to be solved. In this study, a waste biomass of reed straw is pretreated by using a new strategy-hydrothermal treatment instead of pickling and successfully transformed to hard carbon materials through subsequent carbonization process. The reed straw carbonized at 1300 °C exhibits an impressively high reversible capacity of 372.0 mAh g−1 with excellent initial coulombic efficiency of 77.03% and outstanding cycling stability. Significantly, the sodium storage mechanism in our electrodes is mainly summarized into two models. Moreover, we find the interlayer spacing of graphite-like nanocrystal of obtained hard carbon influences the sodium ion diffusion ability, thereby affecting the rate performance. Our work offers a simple and eco-friendly way for converting biomass to highly capacity carbon as well as a towardly anode material for sodium-ion batteries, which will open up new avenues of other biomass carbon materials with promising applications.

By means of developing a novel titanium dissolving slow hydrolysis method, a diphase Li4Ti5O12-TiO2 nanocomposite sphere material with high grain boundary density was synthesized in situ, which showed improved rate capability and specific capacity when being applied to lithium-ion battery as an anode material. Due to a large amount of heat released during the dissolution of titanium powder, the sample with the primary structural morphology of nanosphere has the highest specific surface area of 124.6 m2g−1, and yielded good electrochemical performance in terms of high capacity (274 mAhg−1 at a current density of 0.5 C) as well as excellent cycling stability (135 mAhg−1 at a current density of 5 C up to 200 cycles). The outstanding electrochemical performance of the Li4Ti5O12-TiO2 nanocomposite could be a result of the improved morphology, including the presence of high grain boundary density among the nanoparticles, Ti3+ layering on each nanocrystal, and larger grain boundary interface areas. On this basis, the electronic transport properties were adjusted through interface design and nanometer-scale interface spacing, so as to provide more channels for the Li+ ion insertion/extraction reactions. As a highly effective way to improve the electrochemical properties of Li4Ti5O12-TiO2, a titanium dissolving slow hydrolysis mechanism promising to be the advanced batteries with denser volumetric energy, higher surface stability and longer cycle life than the common TBT hydrolysis in electrode materials. Therefore, it is ideal for being used as a high rate performance anode material for lithium-ion batteries.

Ti3+ self-doped spinel Li4Ti5O12 (LTO) particles were synthesized through a facile electrochemical modification route in NaCl-KCl molten salt electrolysis, and the formation mechanism is explored. Alternating Ti3+ self-doping significantly improves the electrochemical performance of the spinel Li4Ti5O12 (LTO) particle, especially at high charge/discharge rates. According to the report, LTO, once introduced with oxygen vacancies or Ti3+, will decrease the band gap about to 1.54 eV, which can dramatically improve the inherent electronic conductivity. Through the molten salt electrochemical modification technique, the Ti3+ species will be doped onto the surface of LTO, which was confirmed through transmission electron microscopy with EPR (namely electron spin resonance) spectra, X-ray photoelectron spectroscopy, X-ray analysis. As anodes in lithium-ion batteries (LIBs), the spinel Li4Ti5O12 (LTO) particle electrode with self-doped Ti3+ can deliver stable discharge capacities of 168, 152, 131, 120, 102, 93 and 78 mAh g−1 at different rates of 0.5, 1, 5, 10, 15 and 20C, respectively. Meanwhile, like pure spinel LTO, they also carry strong cycling stability and demonstrate the capacity retention of 92.0%, though after 900 cycles under 5C. Our results indicate that pure-phase LTO is prepared by a molten salt method, and it is then electrochemically modified by a constant current to obtain conductive Ti3+. Self-doped spinel Li4Ti5O12 particles are a good alternative to facilitate the transfer of electrons, especially under high-rate conditions, because it shows good electronic and ionic conductivities. In addition, the molten salt synthesis and the electrochemical modification steps of this method are conducted in the same reactor with a simple process, strong operability and environmental friendly process.

Lithium sulfur battery has a theoretical specific capacity of up to 1600 mA h g−1, which has a significant prospect. However, the shuttle effect of polysulfide, the low conductivity of sulfur and the serious volume change during charging and discharging process hinder the commercial application of lithium-sulfur batteries (LSBs). Here, the flower-like ball-in-ball NiCo2S4@MoS2 heterojunction composites were fabricated as the effective sulfur host in LSBs, which exhibited high specific capacity and durable cyclic life. The NiCo2S4 made up ball-in-ball structure offering more chemisorption sites to limit lithium polysulfide (LiPS) dissolution, and the MoS2 nanosheets grow in the surface of NiCo2S4 sphere to form three dimensional flower structure for accelerating the kinetics of LSBs redox reaction. Additionally, the specific hollow structure also availably alleviated the volume change during charging and discharging. Based on these merits, the NiCo2S4@MoS2 electrode with a sulfur content of 74% possessed an initial specific capacity of 1118 mAh g−1 at 0.1 C, and still had a reversible capacity of 865 mAh g−1 after 300 cycles. Even at a high rate of 5 C, the capacity of 467 mAh g−1 could still be achieved after 500 cycles.

Metal doping is an effective way to improve the electrochemical properties of titanates. In this work, Ba-site substituted Ba 0.9 M 0.1 Li 2 Ti 6 O 14 (M = K, Zn, La) are synthesized to fabricate high performance titanate anode for lithium-ion batteries. Electrochemical evaluations reveal that introducing metal doping at Ba-site can result in higher ionic/electronic conductivity. As a result, Ba 0.9 M 0.1 Li 2 Ti 6 O 14 exhibits enhanced lithium storage capability. Especially for Ba 0.9 La 0.1 Li 2 Ti 6 O 14 , it shows the best electrochemical performance with a high reversible charge capacity of 151.3 mAh g −1 and high capacity retention of 94.21% at a current density of 100 mA g −1 . For comparison, the pristine BaLi 2 Ti 6 O 14 only exhibits a reversible charge capacity of 128.5 mAh g −1 with the capacity retention of 80.06% after 100 cycles. Further, the lithium storage process is investigated in detail by in-situ structural observation, which reveals a maximum volume expansion of 1.9% for Ba 0.9 La 0.1 Li 2 Ti 6 O 14 during charge-discharge cycle. It shows that Ba 0.9 La 0.1 Li 2 Ti 6 O 14 is a possible material with high structural reversibility for lithium storage.

Using Ag, Pb and Al as dopants, Ba 0.95 M 0.05 Li 2 Ti 6 O 14 is fabricated as advanced anode candidate for repeated lithium storage. Owing to smaller ionic radius, Ag + , Pb 2+ and Al 3+ are successfully introduced into the lattice of BaLi 2 Ti 6 O 14 , which results in the formation of high purity Ba-site doped Ba 0.95 M 0.05 Li 2 Ti 6 O 14 (M = Ag, Pb, Al). Compared with the pristine sample, M-doped BaLi 2 Ti 6 O 14 exhibits higher reversible capacity, better rate capability and superior cyclability. Especially for Ba 0.95 Ag 0.05 Li 2 Ti 6 O 14 , it presents the best electrochemical property among all the as-prepared samples. It can deliver a high reversible charge capacity of 149.1 mAh g −1 after 100 cycles at the current density of 100 mA g −1 with capacity retention of 92.27%. In contrast, BaLi 2 Ti 6 O 14 only provides a lithium storage capacity of 126.9 mAh g −1 with capacity retention of 80.83%. In addition, its high structural stability and electrochemical reversibility are also demonstrated by in-situ X-ray diffraction observation. All these evidences show that metal doping may be an effective method to enhance the lithium storage capability of BaLi 2 Ti 6 O 14 . Especially for Ba 0.95 Ag 0.05 Li 2 Ti 6 O 14 , it can be used as possible anode candidate for rechargeable batteries.

With the Pb doping content at Sr-site increasing, a series of Sr 1-x Pb x Li 2 Ti 6 O 14 (x = 0, 0.25, 0.50, 0.75, 1.0) are synthesized by a simple solid-state reaction. It is found that the reversible capacity and rate capability experience a parabolic course from SrLi 2 Ti 6 O 14 to PbLi 2 Ti 6 O 14 . Among all the as-prepared samples, Sr 0.5 Pb 0.5 Li 2 Ti 6 O 14 shows the best cycling and rate properties. It delivers an initial charge capacity of 163.2 mAh g −1 at 100 mA g −1 with the capacity retention of 96.08% after 100 cycles. In addition, it can also deliver a reversible capacity of 141.8 mAh g −1 at 700 mA g −1 . The superior electrochemical properties of Sr 0.5 Pb 0.5 Li 2 Ti 6 O 14 are attributed to the reduced charge transfer resistance and increased lithium-ion diffusion coefficient after doping. Besides, in-situ X-ray diffraction is also performed to investigate the lithium-ion insertion/extraction behaviors of SrLi 2 Ti 6 O 14 , Sr 0.5 Pb 0.5 Li 2 Ti 6 O 14 and PbLi 2 Ti 6 O 14 . The observed results confirm that Sr 0.5 Pb 0.5 Li 2 Ti 6 O 14 has good structural stability and reversibility for repeated lithium storage.

Spinel LiCrTiO4 is synthesized via sol-gel pretreatment and subsequent solid state reaction at different calcining temperatures. Structural observation and electrochemical evaluation show that 800 °C is a suitable calcining temperature for LiCrTiO4 preparation. Compared with samples prepared at other temperatures, LiCrTiO4 formed at 800 °C exhibits better electrochemical performance with the capacity retention of 92.2% at 100 mA g−1 after 80 cycles. Even cycled at a higher current density of 500 mA g−1 in 0.0-3.0 V, LiCrTiO4 prepared at 800 °C still shows excellent cycling performance with a reversible capacity of 226.7 mAh g−1 after 80 cycles. Ex-situ valence analysis reveals that the high lithium storage capacity in LiCrTiO4 between 0.0 and 3.0 V is attributed to the reversible redox process of Ti4+/Ti3+ and Cr3+/Cr2+ couples. In addition, quasi zero-strain characteristic of LiCrTiO4 during lithiation is also demonstrated by in-situ and ex-situ structural observations. Therefore, LiCrTiO4 exhibits high structural stability and electrochemical reversibility as anode material for rechargeable lithium-ion batteries.

In this paper, carbon coated Li5Cr9Ti4O24 is prepared by using cystine as carbon source, which results in the formation of carbon co-doped with nitrogen/sulfur (CNS) coating layer after pyrolysis. Compared with carbon free Li5Cr9Ti4O24, the resulting Li5Cr9Ti4O24@CNS exhibits enhanced lithium storage capability. Cycled at 500 mA g−1, it can be found that carbon free Li5Cr9Ti4O24 can only deliver the reversible capacity of 97.8 mAh g−1 with capacity retention of 80.7% after 200 cycles. In contrast, Li5Cr9Ti4O24@CNS can maintain the reversible lithium storage capacity of 111.4 mAh g−1 with capacity retention of 91.9% after 200 cycles. This improvement is attributed to the introduction of nitrogen/sulfur dual-doped carbon coating layer, which significantly enhances the electronic/ionic conductivity and reduces the charge-transfer resistance of Li5Cr9Ti4O24. Hence, Li5Cr9Ti4O24@CNS may be a promising anode candidate for lithium-ion batteries.

In this work, a novel lithium storage material Li 5 Cr 9 Ti 4 O 24 is reported as anode material for rechargeable lithium-ion batteries. We prepare Li 5 Cr 9 Ti 4 O 24 by two different routes, sol-gel method and solid state reaction. Li 5 Cr 9 Ti 4 O 24 nanocrystalline can be achieved by sol-gel method, while solid state reaction delivers micro-sized product. Electrochemical results show that Li 5 Cr 9 Ti 4 O 24 nanocrystalline exhibits reduced charge transfer resistance, decreased redox polarization and improved lithium-ion diffusion coefficient compared with micro-sized product. As a result, Li 5 Cr 9 Ti 4 O 24 nanocrystalline shows excellent lithium storage capability with 100% capacity retention after 200 cycles. Cycled at 600 mA g −1 , it still can deliver a charge specific capacity of 110.3 mAh g −1 . In contrast, micro-sized Li 5 Cr 9 Ti 4 O 24 only reveals the reversible capacity of 66.8 mAh g −1 at the same current density. In addition, Li 5 Cr 9 Ti 4 O 24 nanocrystalline also shows outstanding structural stability for repeated lithium storage. In-situ structural observation reveals that the entire volume expansion of Li 5 Cr 9 Ti 4 O 24 is only 0.62% during the charge/discharge process, which is similar with the zero-strain Li 4 Ti 5 O 12 . Therefore, Li 5 Cr 9 Ti 4 O 24 nanocrystalline can be used as high performance anode material for lithium-ion batteries.

In this paper, a series of Li 3-x Na x V 2 (PO 4 ) 3 (0 ≤ x ≤ 3) are prepared by a solid state reaction and systematically evaluated as anode materials for lithium-ion batteries. Structural analysis shows that the phase structure of Li 3-x Na x V 2 (PO 4 ) 3 changes along with the evolution of Na content. Charge-discharge tests exhibit that Li 3 V 2 (PO 4 ) 3 shows the highest initial charge specific capacity as high as 88.3 mAh g −1 among all the seven samples, and the reversible capacity is kept at 68.3 mAh g −1 after 45 cycles, corresponding to 77.3% of the initial charge capacity. With increasing of Na content in Li 3-x Na x V 2 (PO 4 ) 3 , the as-obtained sample show poorer lithium storage capability than Li 3 V 2 (PO 4 ) 3 . As a result, Na 3 V 2 (PO 4 ) 3 shows the inferior cycling performance than other Li 3-x Na x V 2 (PO 4 ) 3 . It can only deliver a reversible capacity of 20.9 mAh g −1 after 45 cycles, corresponding to 45.9% of the initial charge capacity. In-situ X-ray diffraction observations demonstrate that the poor electrochemical property of Na 3 V 2 (PO 4 ) 3 anode is due to the irreversible structural evolution during charge-discharge process. Therefore, reducing the Na 3 V 2 (PO 4 ) 3 phase in as-obtained sample is a feasible route to improve the lithium storage capability of Li 3-x Na x V 2 (PO 4 ) 3 .

A series of Mg 2+ doped Li 2 Na 2 Ti 6 O 14 in the form of Li 2-x Mg x Na 2 Ti 6 O 14 (x = 0.0, 0.05, 0.1, 0.15, 2.0) are successfully synthesized via a solid-state method. Phase structure and surface morphology analyses show that all samples maintain high purity and low dose of Mg 2+ doping does not change the crystal structure and surface morphology of Li 2 Na 2 Ti 6 O 14 . According to the Rietveld refinement result, it is known that Mg 2+ takes the tetrahedral 8i sites shared with Li + in the structure. Galvanostatic charge/discharge tests demonstrate that Li 1.95 Mg 0.05 Na 2 Ti 6 O 14 exhibits higher reversible capacity (264.6 mAh g −1 ) and better cycling performance (capacity retention of 82.7% after 50 cycles) than other materials. Even cycled at high current density of 500 mA g −1 , Li 1.95 Mg 0.05 Na 2 Ti 6 O 14 still provides the specific capacity of 167.4 mA g −1 after 100 cycles, indicating that low dose of Mg 2+ doping can effectively improve the lithium storage capability of Li 2 Na 2 Ti 6 O 14. The enhanced electrochemical properties are contributed to the improved electronic conductivity and ionic diffusion coefficient of Li 2 Na 2 Ti 6 O 14 via Mg 2+ doping. Besides, the lithiation/delithiation behavior of Li 1.95 Mg 0.05 Na 2 Ti 6 O 14 is also studied by homemade in-situ X-ray diffraction device, which reveals that Li 1.95 Mg 0.05 Na 2 Ti 6 O 14 exhibits high structural and electrochemical reversibility as lithium storage material.

This work presents an electrochemical study of Ti 3+ and Al 3+ in the NaCl-KCl-AlCl 3 -Ti 2 O 3 at 1123K. Transient electrochemical techniques show that Ti 3+ ions are reduced to Ti metal by a two-step mechanism involving the exchanges of one and two electrons. The electrochemical co-reduction of Ti 3+ and Al 3+ in the NaCl-KCl-AlCl 3 -Ti 2 O 3 melts at 1123 K was performed. Cyclic voltammetry and square wave voltammetry were applied using a molybdenum electrode to investigate the reduction behavior of Ti 3+ and Al 3+ and to identify the Ti-Al alloys. A series of redox signals corresponding to different Ti-Al alloys were observed. Potentiostatic electrolysis was conducted using a molybdenum electrode to prepare the Ti-Al alloys. The obtained deposits were characterized by SEM-EDS and XRD. Compounds Layers of TiAl 3 and TiAl 2 were generated via potentiostatic electrolysis.