Fabrication of attractive Li4SiO4 pebbles with modified powders synthesized via surfactant-assisted hydrothermal method

Li₄SiO₄ pebbles have been widely studied as attractive tritium breeding materials in the fusion reactor blanket of international thermonuclear experimental reactor (ITER). In this work, surfactant-assisted hydrothermal method was first employed to prepare ultrafine ceramic powders for fabricating attractive Li₄SiO₄ pebbles. SEM analysis revealed that the introduction of sodium dodecyl sulfate could eliminate the particle aggregation to prepare monodispersed precursor powders, and thus generated the green bodies of pebble with homogeneous microstructure, which was helpful to eventually obtain high-quality Li₄SiO₄ pebbles. Moreover, the effects of sintering temperature on the grain size, relative density, and crush load of Li₄SiO₄ pebbles were also investigated. Li₄SiO₄ pebbles sintered at 700 °C had a high crush load (average value 27.39 N), small grain size (average value 0.57 μm), satisfactory density (88.13%T.D.) and abundant pore structure, which were expected to show favorable tritium release behavior as a promising tritium breeding material for fusion reactor blanket.     

Hydrothermal synthesis of spherical Li4Ti5O12 material for a novel durable Li4Ti5O12/LiMn2O4 full lithium ion battery

Pure spherical Li₄Ti₅O₁₂ spinel material is quickly synthesized via an efficient hydrothermal procedure. The obtained Li₄Ti₅O₁₂ particle size is about 0.5 µm. The Li₄Ti₅O₁₂ has an initial discharge capacity of 162.2 mA h g⁻¹ and capacity retention of 97.5% after 100 cycles at a rate of 0.2 C. Then, a 2.5 V and long-lasting Li-ion cell with a LiMn₂O₄ cathode and a Li₄Ti₅O₁₂ anode is developed. Electrochemical measurements of the cell indicate that the Li₄Ti₅O₁₂/LiMn₂O₄ full cell, with a weight ratio of 1.5 between cathode and anode, exhibits excellent electrochemical performance, delivering a reversible capacity of 130 mA h g⁻¹ at room temperature. The full cell also exhibits outstanding electrochemical performances at high temperature, as it has an initial discharge capacity of 109.6 mA h g⁻¹, along with a capacity retention rate of 88.9% after 100 cycles at 55 °C.     

Synthesis and electrochemical properties of La-doped Li4Ti5O12 as anode material for Li-ion battery

La-doped Li₄Ti₅O₁₂ was successfully synthesized from Li₂CO₃, La₂O₃ and tetrabutyl titanate by a simple ball milling assisted modified solid-state method. The impact of La-doping on crystalline structure, particle size, morphology and electrochemical performance of Li₄Ti₅O₁₂ was investigated. The samples were characterized by XRD, SEM, galvanostatically charge–discharge and electrochemical impedance spectroscopy. The results demonstrated that the in-situ coated and ball-milling method could decrease the particle size and prevent the aggregation of Li₄Ti₅O₁₂. La-doping obviously improved the rate capability of Li₄Ti₅O₁₂ via the generation of less electrode polarization and higher electronic conductivity. Li_3.95La_0.05Ti₅O₁₂ exhibited a relatively excellent rate capability and cycling stability. At the charge–discharge rate of 0.5 C and 40 C, its discharge capacities were 176.8 mAh/g and 54.7 mAh/g. After 10 cycles, fairly stable cycling performance was achieved without obvious capacity fade at 0.5 C, 1 C, 2 C, 5 C, 10 C, 20 C and 40 C. In addition, compared to Li₄Ti₅O₁₂, Li_3.95La_0.05Ti₅O₁₂ almost did not have the initial capacity loss. It indicated that Li_3.95La_0.05Ti₅O₁₂ was a promising candidate material for anodes in Li-ion battery application.     

Effect of Fe-doping followed by C+SiO2 hybrid layer coating on Li3V2(PO4)3 cathode material for lithium-ion batteries

A novel Li₃V₂(PO₄)₃ composite modified with Fe-doping followed by C+SiO₂ hybrid layer coating (LVFP/C-Si) is successfully synthesized via an ultrasonic-assisted solid-state method, and characterized by XRD, XPS, TEM, galvanostatic charge/discharge measurements, CV and EIS. This LVFP/C-Si electrode shows a significantly improved electrochemical performance. It presents an initial discharge capacity as high as 170.8 mA h g⁻¹ at 1 C, and even delivers an excellent initial capacity of 153.6 mA h g⁻¹ with capacity retention of 82.3% after 100 cycles at 5 C. The results demonstrate that this novel modification with doping followed by hybrid layer coating is an ideal design to obtain both high capacity and long cycle performance for Li₃V₂(PO₄)₃ and other polyanion cathode materials in lithium ion batteries.     

Electrochemical cycling behaviour of lithium carbonate (Li2CO3) pre-treated graphite anodes – SEI formation and graphite damage mechanisms

Graphite electrode surfaces were treated using a simple process of sedimentation in aqueous solutions containing 0.5 and 1.0 wt.% Li₂CO₃ with particle sizes of ∼1–2 μm. During the first cycle of voltammetry tests (vs. Li/Li⁺), the graphite surface was subjected to electrochemical degradation as a result of fracture and removal of near-surface graphite particles. Surface degradation was accompanied by a 0.4% strain in the graphite lattice as determined by in situ Raman spectroscopy. Pre-treated electrodes experienced a capacity drop of 3% in the first cycle, compared to a 40% drop observed in case of untreated graphite electrodes. After testing for 100 cycles, a capacity of 0.54 mAh cm⁻² was recorded for the pre-treated electrodes as opposed to a significant drop to 0.11 mAh cm⁻² for the untreated graphite. Cross-sectional HR-TEM indicated that the SEI formed on the pre-treated electrodes primarily consisted of Li₂CO₃ crystals of 14.6 ± 6.9 nm in size distributed within an amorphous matrix. The results suggested that the Li₂CO₃ enriched SEI formed on the pre-treated electrodes reduced the intensity of solvent co-intercalation induced surface damage. It is proposed that the Li₂CO₃ enriched SEI facilitated Li⁺ diffusion and hence improved the capacity retention during long-term cycling.     

Low-temperature sintered MgWO4–CaTiO3 ceramics with near-zero temperature coefficient of resonant frequency

The phases, microstructure, composition analysis and microwave dielectric properties of (1 ? x)MgWO₄–xCaTiO₃ ceramics with Li₂CO₃–4H₃BO₃ additions prepared by solid-state reaction method have been investigated by using X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy and advantest network analyzer. The τ_f of (1 ? x)MgWO₄–xCaTiO₃ were dependent on phase constitutions. The microwave dielectric properties of 0.91MgWO₄–0.09CaTiO₃ ceramics with Li₂CO₃–4H₃BO₃ were characterized, the results indicated that the ?_r and Q × f were associated with the sintering temperature and amount of Li₂CO₃–4H₃BO₃. The sintering temperature of ceramics was reduced to 950 °C from 1150 °C and τ_f was modified to 0 ppm/°C with good Q × f. Addition of 5.0 wt% Li₂CO₃–4H₃BO₃ in 0.91MgWO₄–0.09 CaTiO₃ ceramics sintered at 950 °C showed excellent dielectric properties of ?_r = 15.5, Q × f = 20,780 GHz (f = 7.1 GHz) and τ_f ～ 0 ppm/°C. The material has a chemical compatibility with silver, making it a very promising candidate materials for LTCC applications.     

Electrochemical characterization of P2-type layered Na2/3Ni1/4Mn3/4O2 cathode in aqueous hybrid sodium/lithium ion electrolyte

P2-type layered Na_2/3Ni_1/4Mn_3/4O₂ has been synthesized by a solid-state method and its electrochemical behavior has been investigated as a potential cathode material in aqueous hybrid sodium/lithium ion electrolyte by adopting activated carbon as the counter electrode. The results indicate that the Na⁺/Li⁺ ratio in aqueous electrolyte has a strong influence on the capacity and cyclic stability of the Na_2/3Ni_1/4Mn_3/4O₂ electrode. Increase on the Li⁺ content leads to a shift of the redox potential towards a high value, which is favorable for the improvement of the working voltage of the layered material as cathode. It is found that the coexistence of Na⁺ and Li⁺ in aqueous electrolyte can improve the cyclic stability for the Na_2/3Ni_1/4Mn_3/4O₂ electrode. A reversible capacity of 54 mAh g⁻¹ was obtained with a high cyclability as the Na⁺/Li⁺ ratio was 2:2. Furthermore, an aqueous hybrid ion cell was assembled with the as-proposed Na_2/3Ni_1/4Mn_3/4O₂ as cathode and NaTi₂(PO₄)₃/graphite synthesized in this work as anode in 1 M Na₂SO₄/Li₂SO₄ (mole ratio as 2:2) mixed electrolyte. The cell shows an average discharge voltage at 1.2 V, delivering an energy density of 36 Wh kg⁻¹ at a power density of 16 W kg⁻¹ based on the total mass of the active materials.     

Synthesis and electrochemical performance of Li4Ti5O12/C composite by a starch sol assisted method

Li₄Ti₅O₁₂/C composite anode materials were synthesized by a simple starch sol assisted method using TiO₂-anatase and Li₂CO₃ as raw materials and soluble starch as carbon source. The influences of calcination temperature and starch amounts on the microstructure and electrochemical performance were systematically investigated. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and constant-current charge/discharge cycling tests. The results showed that the Li₄Ti₅O₁₂/C composite with 10 wt.% starch synthesized at 800 °C for 6 h had homogeneous particle size distribution with an average particle size of 200–300 nm and exhibited the optimal electrochemical performance with specific discharge capacities of 168.5, 160.8, 155.1 and 141.8 mAh g^? 1 at 0.2 °C, 1 °C, 2 °C and 5 °C rates, respectively, and satisfactory cycling stability. It could be attributed to the homogeneous ultrafine particles and in situ carbon coating, which enhanced the electronic conductivity and diffusion of lithium ions in the electrode.     

High temperature CO2 capture performance and kinetic analysis of Na4SiO4 ceramics

Alkali silicate-based ceramics sorbents were regarded as particularly suitable materials for CO₂ capture at high temperatures, however, the CO₂ capture behaviors of Na₄SiO₄ had been seldom investigated. In this work, the Na₄SiO₄ ceramics samples were prepared using the one-step synthesized method, and the CO₂ sorption/desorption performances at high temperatures, the thermal stability, and the cycling stability of Na₄SiO₄ were systematically investigated. It was demonstrated that the maximum CO₂ sorption capacity of SO-3 sample reached 19.4 wt% at 725 °C, and the optimal condition of cycling tests were 750 °C for sorption and 800 °C for desorption based on the sorption/desorption capacity and rate, which exhibited good thermal stability and high cyclic stability. Besides, the kinetic analysis results showed that the diffusion process was the rate-determining step of CO₂ adsorption, which was more dependent on temperature than the chemisorption process. The structure and surface morphology variations were also investigated, it was interesting that there was a special “fish scale” surface structure after the sorption process, revealing that the melting phenomenon happened during the chemisorption reaction process. By comparing with common sorbent Li₄SiO₄, the material and CO₂ capture costs of Na₄SiO₄ were much lower. These results proved that Na₄SiO₄ was expected to be a suitable high temperature CO₂ capture material as a good supplement to alkali silicate-based ceramics sorbents.     

Effects of Li2CO3 addition on the microstructure and magnetic properties of low-temperature-fired NiCuZn ferrites

NiCuZn ferrites doped with 0.5 wt% Bi₂O₃ and different Li₂CO₃ contents (0–0.25 wt%) were sintered at 900 °C. The microstructure and magnetic properties of these materials were investigated. The addition of low-melting-point Li₂CO₃ led to large and uniform grains. However, excess Li₂CO₃ addition produced abnormal grains and many closed pores, thereby reducing density. Permeability initially increased and then decreased at the Li₂CO₃ content of >0.2 wt%. Maximum magnetic flux density (431.1 mT at room temperature, 339.6 mT at 100 °C) and minimum power loss were achieved at 0.2 wt% Li₂CO₃. These findings suggested the suitability of 0.2 wt% Li₂CO₃ for applications in low-temperature co-fired ceramic magnetic power components and modules.     

Improved electromagnetic absorbing properties of Si3N4–SiC/SiO2 composite ceramics with multi-shell microstructure

Porous Si₃N₄–SiC composite ceramic was fabricated by infiltrating SiC coating with nano-scale crystals into porous β-Si₃N₄ ceramic via chemical vapor infiltration (CVI). Silica (SiO₂) film was formed on the surface of rod-like Si₃N₄–SiC grains during oxidation at 1100 °C in air. The as-received Si₃N₄–SiC/SiO₂ composite ceramic attains a multi-shell microstructure, and exhibits reduced impedance mismatch, leading to excellent electromagnetic (EM) absorbing properties. The Si₃N₄–SiC/SiO₂ fabricated by oxidation of Si₃N₄–SiC for 10 h in air can achieve a reflection loss of ?30 dB (>99.9% absorption) at 8.7 GHz when the sample thickness is 3.8 mm. When the sample thickness is 3.5 mm, reflection loss of Si₃N₄–SiC/SiO₂ is lower than ?10 dB (>90% absorption) in the frequency range 8.3–12.4 GHz, the effective absorption bandwidth is 4.1 GHz.     

Highly selective CO2 capture by S-doped microporous carbon materials

S-doped microporous carbon materials were synthesized by the chemical activation of a reduced-graphene-oxide/poly-thiophene material. The material displayed a large CO₂ adsorption capacity of 4.5 mmol g⁻¹ at 298 K and 1 atm, as well as an impressive CO₂ adsorption selectivity over N₂, CH₄ and H₂. The material was shown to exhibit a stable recycling adsorption capacity of 4.0 mmol g⁻¹. The synthesized material showed a maximum specific surface area of 1567 m² g⁻¹ and an optimal CO₂ adsorption pore size of 0.6 nm. The microporosity, surface area and oxidized S content of the material were found to be the determining factors for CO₂ adsorption. These properties show that the as synthesized S-doped microporous carbon material can be more effective than similarly prepared N-doped microporous carbons in CO₂ capture.     

Enhanced electrochemical performance of Li3V2(PO4)3 structurally converted from LiVOPO4 by graphite nanofiber addition

In this work, the structural conversion of LiVOPO₄ to Li₃V₂(PO₄)₃ due to the addition of graphene nanofiber (GNF) was investigated, and the resulting materials were found to exhibit enhanced capacity and cyclability. First, LiVOPO₄ was synthesized using a solid-state method followed by annealing at 900 °C for 12 h under nitrogen atmosphere. Then, the conversion from the triclinic LiVOPO₄ structure to the monoclinic Li₃V₂(PO₄)₃ structure due to the GNF addition was observed. No impurity peak was observed in the X-ray diffraction patterns of LiVOPO₄ or Li₃V₂(PO₄)₃, and the structural conversion caused no defects to form in the resulting Li₃V₂(PO₄)₃ crystallite. Field emission-scanning electron microscope studies clearly demonstrate that larger corroded-structure-like particles formed which were mixed with GNF. This provided both a large active area and fast transport of lithium ions, which afforded enough active sites for simultaneous intercalation of many lithium ions, leading to improved electrochemical properties of the material. Compared with LiVOPO₄, the Li₃V₂(PO₄)₃–GNF showed better properties, such as an improved lithium ion diffusion coefficient, improved cyclability, and smaller impedance. Furthermore, the optimized Li₃V₂(PO₄)₃–GNF (7%) battery showed the best discharge capacity of 181 mA h g⁻¹ at 0.1 C and lithium ion diffusion coefficient of 6.01×10⁻⁹ cm² s⁻¹.     

Kinetics and equilibrium studies from the methylene blue adsorption on diatomite treated with sodium hydroxide

Diatomite was treated with sodium hydroxide to remove impurity in order to improve its performance as an adsorbent. The raw diatomite and purified diatomite were characterized by scanning electron microscopy, energy dispersive X-ray analysis and Brunauer–Emmett–Teller adsorption. It was found that the surface area was in order of 15.87 m² g^− 1 for raw diatomite and 31.35 m² g^− 1 for purified diatomite. Scanning electron microscopy images showed the well-developed porous structure of purified diatomite. Purified diatomite improved a more than tenfold increase in adsorption amount from 1.72 mg g^− 1 to 18.15 mg g^− 1 and removal efficiency from 8.60% to 90.75% for methyelen blue initial concentration 100 ppm respectively. The kinetics studies showed that experiment data followed pseudo-second-order model better. The equilibrium data was fitted to Langmuir and Freundlich adsorption isotherms and was found that Langmuir model presented the best fit, showing maximum monolayer adsorption capacity of 27.86 mg g^− 1. The thermodynamic parameters such as the standard enthalpy, standard entropy and standard free energy were evaluated. The obtained results indicated the adsorption of methylene blue onto diatomite treated with sodium hydroxide is endothermic and spontaneous process and confirmed the applicability of this purified inorganic material as an efficient adsorbent for basic dyes.     

Thermodynamics and regeneration studies of CO2 adsorption on multiwalled carbon nanotubes

Multiwalled carbon nanotubes (CNTs) were fabricated and modified by 3-aminopropyl-triethoxysilane (APTS) solutions to study thermodynamics and regeneration of CO₂ adsorption from gas streams. The CO₂ adsorption capacities of CNTs and CNT(APTS) decreased with temperature indicating the exothermic nature of adsorption process while the thermodynamic analysis gave low isosteric heats of adsorption, which are typical for physical adsorption. The cyclic CO₂ adsorption on CNT(APTS) showed that the adsorbed CO₂ could be effectively desorbed via thermal treatment at 120 °C for 25 min while the adsorbed CO₂ due to physical interaction could be effectively desorbed via vacuum suction at 0.145 atm for 30 min. If a combination of thermal and vacuum desorption was conducted at 120 °C and 0.145 atm, the time for effectively desorbing CO₂ could be further shortened to 5 min. The adsorption capacities and the physicochemical properties of CNT(APTS) were preserved during 20 cycles of adsorption and regeneration. These results suggest that the CNT(APTS) can be stably employed in prolonged cyclic operation and they are thus possibly cost-effective sorbents for CO₂ capture from flue gases.     

Preparation of Li4SiO4-xLi2O powders and pebbles for advanced tritium breeders

Li₄SiO₄ pebbles and Li₂O pebbles have been considered as the potential candidates for tritium breeders. Li₂O exhibits higher lithium density whereas worse lithium loss and hygroscopicity compared with Li₄SiO₄. It is anticipated to obtain an advanced breeder by combining Li₄SiO₄ with Li₂O. The coexistence of Li₄SiO₄ and Li₂O powders could not be obtained by solid state reaction using Li₂CO₃ as lithium source, while the biphasic Li₄SiO₄-xLi₂O (x=0.1, 0.2, 0.3, 0.4) powders were prepared by sol-gel method in this experiment. Meanwhile, the biphasic Li₄SiO₄-xLi₂O pebbles were fabricated by a wet method for the first time. The Li₂O aggregated at the grain boundaries and promoted the grain growth of the Li₄SiO₄. The grain size and the crush load of the Li₄SiO₄-0.3Li₂O pebbles reached 32.3 µm and 46.5 N, respectively.     

Covalent grafting of aminated compounds on Vulcan XC72R by melamine in situ diazotization

The immobilization of 2,4-diamino-1,3,5-triazine on carbon Vulcan XC72R surface was achieved through the in situ diazotization of melamine. The resulting grafted species represent 2.3 wt.% of the modified material and are thermally stable up to 265 °C. Nitrogen adsorption isotherms show that the carbon microporosity decreased after modification translating in a 25% decrease of the BET surface area. X-ray photoelectron spectroscopy data suggest the presence of 2,4-diamino-1,3,5-triazine groups at the surface by bonding through a carbon–carbon bond and/or by an azo bridge. These materials were evaluated as CO₂ sorbents by thermal swing adsorption in a thermogravimetric analyzer. At 40 °C, the modified powders displayed a maximal adsorption capacity of 0.23 mmol/g that is smaller than the initial unmodified material. Nonetheless adsorption capacity of the grafting groups helps to improve the selectivity of the materials although physisorption seems to be the main mechanism for CO₂ capture.     

Temperature stability and high-Qf of low temperature firing Mg2SiO4–Li2TiO3 microwave dielectric ceramics

In this work, a series of low-temperature-firing (1−x)Mg₂SiO₄–xLi₂TiO₃–8 wt% LiF (x = 35–85 wt%) microwave dielectric ceramics was prepared through conventional solid state reaction. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed that the Li₂TiO₃ phase was transformed into cubic phase LiTiO₂ phase and secondary phase Li₂TiSiO₅. Partial substitution of Mg²⁺ ions for Ti³⁺ ions or Li⁺Ti³⁺ ions increased the cell volume of the LiTiO₂ phase. The dense microstructures were obtained in low Li₂TiO₃ content (x ≤ 65 wt%) samples sintered at 900 °C, whereas the small quantity of pores presented in high Li₂TiO₃ content (x ≥ 75 wt%) samples sintered at 900 °C and low Li₂TiO₃ content (x = 45 wt%) sintered at 850 and 950 °C. Samples at x = 45 wt% under sintering at 900 °C for 4 h showed excellent microwave dielectric properties of ε_r = 10.7, high Q × f = 237,400 GHz and near-zero τ_f = − 3.0 ppm/°C. The ceramic also exhibited excellent chemical compatibility with Ag. Thus, the fabricated material could be a possible candidate for low temperature co-fired ceramic (LTCC) applications.     

SBA-15-supported ionic liquid compounds containing silver salts: Novel mesoporous π-complexing sorbents for separating polyunsaturated fatty acid methyl esters

Novel π-complexing sorbents were prepared by covalently immobilizing ionic liquids (ILs) onto mesoporous SBA-15 using a one-pot sol–gel process followed by coating these SBA-15-supported IL compounds with silver salts. The mesoporous π-complexing sorbents were characterized by small angle X-ray scattering (SAXS), FTIR, TEM, SEM, nitrogen adsorption desorption isotherm, NMR, and nitrogen elemental analysis. Two advantages were obtained using these novel mesoporous π-complexing sorbents versus the traditional π-complexing sorbents formed by directly anchoring silver salts onto silica gel. (1) Higher extraction capacities were found. The extraction capacity for the polyunsaturated fatty acid methyl ester (PUFAME), methyl all-cis-5,8,11,14,17-eicosapentaenoate (20:5 or EPA), was 195 mg/g sorbent using the mesoporous AgBF₄/SBA-15 · IL · PF₆ sorbent. The capacity decreased to 121 mg/g sorbent with microporous complexing sorbent AgBF₄/SiO₂ · IL · PF₆. (2) Better reusability was also achieved. The supported IL phase immobilized and retained silver salt on SBA-15 due to the interaction between the ionic liquid’s imidazolium cations and silver ions. Eight successive sorption runs with the AgBF₄/SBA-15 · IL · PF₆ sorbent showed a satisfactory reusability. The traditional π-complexing sorbent has a silver salt directly anchored on silica without the supported ionic liquid phase. Higher silver leaching into organic solution occurred from the AgBF₄/SBA-15 sorbent determined by ICP-AES. The combined percentage (wt%) of the omega-3 PUFAMEs: 20:5 and methyl all-cis-4,7,10,13,16,19-docosahexaenoate (22:6 or DHA) stripped from the AgBF₄/SBA-15 · IL · PF₆ by 1-hexene was significantly enriched from 18% in the original cod liver oil to 90.5%.     

Thermal cycling induced capacity enhancement of graphite anodes in lithium-ion cells

Graphite electrodes were electrochemically cycled in Li-ion cells at 50 and 60 °C in order to determine the changes in their surface properties in comparison to the electrodes tested at 25 °C. A 17% drop in planar capacity occurred during the first cycle at 60 °C compared to a 40% at 25 °C and reduced the amount of damage that occurred to graphite due to a rapidly formed solid electrolyte interphase (SEI). During the following cycles, a planar capacity of 3.11 ± 0.12 mAh cm⁻² was attained at 60 °C rather than 0.53 ± 0.03 mAh cm⁻² at 25 °C. The SEI layer formed at 60 °C predominantly consisted of Li₂CO₃ and was devoid of residual LiClO₄ detected at 25 °C. At 25 °C, the diffusion coefficient of Li⁺ (D_Li⁺) was calculated as 1.07 × 10⁻⁸ cm² s⁻¹, whereas at 60 °C, D_Li⁺ increased to 3.25 × 10⁻⁸ cm² s⁻¹. A pre-treatment conducted at 60 °C enhanced the cyclic performance of graphite subsequently cycled at 25 °C; a Li₂CO₃-enriched SEI, generated during the 60 °C pre-treatment, covered the graphite surface uniformly and resulted in a 28% increase in battery capacity at 25 °C.