Electrodeposition Of Li-Cu Alloy From Ionic Liquid

The specific capacity of lithium being used as Li-ion battery anode materialis3860mAh/g. However, the formation of lithium dendrit occurs duringcharging，it will degrade the performance of the battery. In this study, Li-Cualloy coating was prepared by electrodepositon from ionic liquid. If Li-Cu alloyis used as anodic electrode, after lithium dissolves during discharging, thecopper framework was left, which could hinder the formation of lithium dendrit.Consequently, the safty of batteries was ensured.1-Ethyl-3-methyllimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm]-[TFSI]) ionic liquid was used as the solvent for deposition of Li-Cu alloy. Thedeposition of lithium was studied using cyclic voltammogram(CV). It was foundthat addition of LiTFSI enlarged the electrochemical window of [EMIm][TFSI],which made the deposition of lithium realized. Silver-gray lithium coating withgood adhesion was obtained from [EMIm][TFSI]. As N-methyl-2-pyrrolidone(NMP) being chosen as cosolvent, the depositon of Cu from[EMIm][TFSI]+NMP(volum ratio2:1) was studied using CV. The result showedthat deposition of Cu was an irreversible diffusion controlled electrochemicalprocess. Dark red uniform copper coating was obtained.The effects of deposition parameters on appearance and lithium content ofLi-Cu alloy coating from [EMIm][TFSI]+NMP(volume ratio2:1) were studiedunder different deposition mode. Controlled-current electrodepositon wasstudied，and it was found the content of lithium decreased with the temperatureincreasing and the current density decreasing. The Li/Cu molar ratio had noeffect on lithium content when the concentration of lithium was constant. Basingon the results, it was thought the codeposition of Li-Cu was regular codeposition.The invstigation of the Li-Cu alloy micromorphology showed that as the contentof copper increased, the coating became smoother, and better copper frameformed. Then the deposition parameters of controlled-potentialelectrodeposition of Li-Cu alloy coating were studied. The results showed thecontent of lithium decreased with the temperature increasing and the morepositive potential being applied. A better Li-Cu alloy coating with high lithiumcontent (about50at.%) could be obtained at room temperature when the appliedpotential was-3~-3.5V. It was found a3D structure consisting of many sliceswas obtained, and a perfect copper frame was seen on the deposit that obtained at-3.5V after the lithium dissolved. The deposition of Li-Cu alloy coating wasalso investigated using pulse voltage. It was found the lithium content increasedwith average voltage becoming higher. The effects of frequency and duty ratioon the lithium content were not regular. Meanwhile, the structure of depositobtained was similar with the structure of the deposit obtained by controllingpotential. The condition of obtaining a finer deposits with about50at.%lithiumwere average voltage3V, frequency1kHz, and duty ratio50%.Basing on the XRD and XPS results, it was supposed the deposit consistedof metallic lithium and copper, and they kept each chemical properties. Li-Cualloy may be a mechanical mixture. The CV was used to investigatecodeposition of Li-Cu alloy from [EMIm][TFSI]+NMP(volume ratio2:1). It wasseen clearly there were two reduction peaks which represented deposition ofcopper and codeposition of lithium and copper, separately. The depositionpotential of lithium shifted to more positive potential obviously, which indicatedexistence of copper made deposition of lithium more easily. The CV study alsodemonstrated codeposition of Li-Cu alloy was an irreversible electrochemicalprocess under control of diffusion. The prepared Li-Cu alloy was used as anodicmaterial to make the Li-ion batteries. The test results of the batteries showedthat Li-Cu alloy has the ability of intercalation/deintercalation lithium.