The feasibility for natural graphite to replace artificial graphite in organic electrolyte with different film-forming additives

The feasibility for natural graphite(NG)to replace artificial graphite(AG)in organic electrolytes with different additives are investigated.Although the strong film-forming additives contributes to form robust solid electrolyte interphase(SEI)film on graphite particle surface,great differences in gas evolution,lithium inventory loss and other side reactions are observed.Lithium bis(oxalato)borate(Li BOB)and fluoroethylene carbonate(FEC)are found more effective and the combination shows to be more promising.In the optimized electrolyte,natural graphite anode exhibits excellent long-term cycling capability.After 800 cycles at high temperature,the capacity retention is comparable to that using artificial graphite.The mechanisms for the capacity-fading of the full cells with AG and NG anode are investigated by ICP,SEM and polarization studies.The results shows that NG electrode consumes more active lithium due to the rough surface and larger volume expansion.The rapid capacity-fading in the initial 100 cycles is related to the instability of the SEI film aroused from large volume expansion.The systematic analysis is inspiriting for the development of high performance lithium ion batteries with reduced cost.

Carbide derived carbon electrode with natural graphite addition in magnesium electrolyte based cell for supercapacitor enhancements

Herein,we have presented a supercapacitor based on carbide derived carbon（CDC） electrode with natural graphite（NG） addition.The capacitor was analyzed at 22°C by cyclic voltammetry,galvanostatic charge-discharge and impedance techniques using a 0.5 mol/L of magnesium（II）bis（trifluoro methanesulfonyl） imide（Mg TFSI） in ethylene carbonate-propylene carbonate（EC ：PC = 1 ：1,v/v） as electrolyte.The results conclude that the CDC cell enhancements have been proven by the composite electrode（5%–30% NG to CDC） especially on the cell efficiency and voltage i.e.,the CDC cell around 2.5 V limit was improved.An obtainable specific capacitance,real power and energy density are 15 F g-1,1.2 k W kg-1and 15 Wh kg-1,respectively.

A Novel Modification Approach for Natural Graphite Anode of Li-ion Batteries

To improve the rate capability and cyclability of natural graphite anode for Li-ion batteries,a novel modification approach was developed.The modification approach included two steps:(a)high-energy ball milling in a rotary autoclave containing alumina balls,H_3PO_4 and ethanol;(b)coating with pyrolytic carbon from phenlic resin.The treated graphite shows obvious improvement compared with the original natural graphite in electrochemical properties such as cyclability and rate capability,especially at high current density.The primary reasons leading to the improvement in rate capability and cyclability are that the diffusion impedance of Li^+ in graphite is reduced due to the fact that P filtered into graphite layers can mildly increase interlayer distances,and the fact that the structural stability of graphite surface is enhanced since the coated pyrolytic carbon can depress the co-intercalation of solvated lithium ion.

Cost-effective natural graphite reengineering technology for lithium ion batteries

Graphite tailings produced by natural graphite is usually regarded as garbage to be buried underground,which would result in a certain waste of resources.Here,in order to explore the utilization of natural graphite tailings(NGT),a liquid-polyacrylonitrile(LPAN)is used to modify the NGT fragments and aggregate them together to form secondary graphite particles with low surface area and high tap density.Moreover,the modified NGT show much better electrochemical performances than those of original one.When tested in full cells coupled with NMC532 cathode,the material achieves a high rate capability and cycle stability at the cutoff voltage of 4.25 V as well as 4.45 V,which maintains 84.32%capacity retention after 500 cycles at 1 C rate(4.25 V),higher than that of the pristine one(73.65%).The enhanced performances can be attributed to the use of LPAN to create a unique carbon layer upon graphite tailings to reconstruct surface and repair defects,and also to granulate an isotropic structure of secondary graphite particles,which can help to weaken the anisotropy of Li^(+)diffusion pathway and form a uniform,complete and stable solid-electrolyte-interface(SEI)on the surface of primary NGT fragments to promote a fast Li+diffusion and suppress lithium metal dendrites upon charge and discharge.

The evolution of coal, examining the transitions from anthracite to natural graphite: a spectroscopy and optical microscopy evaluation

Coal-derived natural graphite(CDNG)has multiple industrial applications.Here,ten metamorphic coals from anthracite to CDNG were obtained from Lutang and Xinhua in the Hunan Province and Panshi in the Jilin Province.Bulk characterization(proximate and ultimate analyses,X-Ray powder diffraction(XRD),and powder Raman spectroscopy),along with optical microscopy,scanning electron microscope(SEM)and micro-Raman spectroscopy were utilized to examine the transitions from anthracite to semi-graphite to CDNG.The XRD and Raman spectroscopy data indicate that from anthracite to highly ordered graphite the average crystal diameter(La)and height(Lc)increased from 6.1 and 4.6 nm to 34.8 and 27.5 nm,respectively.The crystalline parameters of the CDNG samples from Panshi and Lutang varied slightly when closer to the intrusive body.Optical microscopy and SEM indicated that in the anthracite samples there were thermoplastic vitrinite,devolatilized vitrinite,and some“normal”macerals.In the meta-anthracite,pyrolytic carbon,mosaic structure,and crystalline tar were present.In the CDNG there were flake graphite,crystalline aggregates,and matrix graphite.The crystalline aggregates show the highest structural ordering degree as determined from Raman spectral parameters(full-width at half maxima(G-FWHM)~20 cm^(−1),D1/(D1+D2+G)area ratio(R2)value<0.5).The flake graphite is less ordered with G-FWHM~28 cm^(−1) and 0.5<R2<1,but a larger grain size(up to 50μm).The mosaic structures were likely the precursors of the matrix graphite through in situ solid-state transformation.The pyrolytic carbon and crystalline tars are the transient phase of gas-state and liquid-state transformations.This study is beneficial to realize the rational utilization of CDNG.

Processing Compressed Expanded Natural Graphite for Phase Change Material Composites

Phase change materials(PCMs)are used in various thermal energy storage applications but are limited by their low thermal conductivity.One method to increase conductivity involves impregnating organic PCMs into highly porous conductive matrix materials.Of these materials,compressed expanded natural graphite(CENG)matrices have received the most attention.Despite this attention,the effect that CENG processing has on PCM saturation and overall matrix thermal conductivity has not been fully investigated.Therefore,the effect of the heat treatment process used to expand intercalated graphite flakes is evaluated here.Higher heat treatment temperatures yielded higher saturation rates and overall saturation at similar matrix porosities.For example,increasing temperature from 300℃to 700℃resulted in approximately 60%-70%increase in pore saturation after 100 minutes of soaking.The exposure time to heat treatment had less of an effect on PCM saturation.The exposure time had negligible effect above 30 min and above 500℃heating temperatures.However,because the expanded graphite was found to oxidize around 700℃,the use of longer exposure time in manufacturing applications can be beneficial if a shortened impregnation time is needed.Heat treatment conditions did not impact thermal conductivity.The composite latent heat of fusion was also reduced approximately proportionally to the PCM mass fraction.A local maximum in axial thermal conductivity was observed at around 83%porosity,which is similar to previous studies.The observed conductivity at this maximum was a factor of 81 times greater than the conductivity of the PCM.

Comparative tribological behavior of friction composites containing natural graphite and expanded graphite

In this study, expanded graphite and natural graphite were introduced into resin-based friction materials, and the tribological behavior of the composites was investigated. The tribo-performance of the two friction composites was evaluated using a constant speed friction tester. The results showed that the expanded graphite composite (EGC) displayed better lubricity in both the fading and the recovery processes. The wear rate of the EGC decreased by 22.43%more than that of the natural graphite composite (NGC). In the fading process, and the EGC enhanced the stability of the coefficient of friction. The recovery maintenance rate of the NGC was 4.66% higher than that of the EGC. It can be concluded that expanded graphite plays an important role in the formation of a stable contact plateau and can effectively reduce the wear.

Influence of particle structure on electrochemical character of composite graphite

The natural graphite has been used as the anode material for Lithium-Ion batteries, because of its low cost, chemical stability and excellent reversibility for Li+ insertion. However, the slow diffusion rate of lithium ion and poor compatibility with electrolyte solutions make it difficult to use in some conditions. In order to solve these problems, an epoxy-coke/graphite composite has been manufactured. The particle of composite carbonaceous material coated on non-graphitizable (hard) carbon matrix. Due to the disordered structure, the diffusion rate of lithium species in the non-graphitzable carbon is remarkably fast and less anisotropic. The process for preparing a composite carbon powder provides a promising new anode material with superior electrochemical properties for Li-ion batteries. The unique structure of epoxy-coke/graphite composite electrodes results in much better kinetics, also better recharge ability and initial charge/discharge efficiency.

Design and 3D Printing of Interdigitated Electrode Structures for High-performance Full Lithium-ion Battery

The tradeoff between energy and power densities is a critical challenge for commercial tape-cast lithium-ion batteries(LIBs).In this study,three-dimensional(3D)LIBs with interdigitated electrode structures are designed and fabricated via 3D printing to overcome this tradeoff.The evolution of battery design from tape-cast thin planar electrodes to interdigitated 3D electrodes is discussed.Numerical simulations based on COMSOL Multiphysics are performed to elucidate the advantages of interdigitated battery design.Interdigitated LIBs composed of comb-like 3D high-voltage LiCoO2(HV-LCO)cathodes and comb-like 3D natural graphite anodes are fabricated via 3D printing.Additionally,printable HV-LCO inks with appropriate rheological properties are developed for 3D printing.HV-LCO half-cells with Li foil as the counter electrode and an interdigitated full battery with NG anodes as the counter electrode are assembled to test the electrochemical performance.The results show that interdigitated full batteries fabricated via 3D printing offer high specific capacities and stable cycling performance.Full batteries with an electrode thickness of 882µm can achieve a high areal capacity of 5.88 mAh·cm−2@0.1 C,an areal energy density of 41.4 J·cm−2,and an areal power density of 41.0 mW·cm−2@1.0 C,which are approximately 10 times the values afforded by conventional tape-cast thin batteries.