Synthesis Of Lithiophilic Framework Based On Nickel Foam And Application In Lithium Metal Secondary Battery

Lithium metal batteries have a high energy density,as one of its important components of the lithium negative electrode,but also has a very high theoretical specific capacity（3860 mAh g-1）and very low electrochemical redox potential（-3.04 V,compared to standard hydrogen electrodes）.Therefore,such batteries are expected to replace lithium-ion batteries and become a mainstream product in the future commercial batteries.However,so far,lithium metal batteries have not been put into actual commercial applications,because lithium metal batteries use lithium metal as a anode,which will cause the disorderly growth of lithium dendrites on the surface,excessive expansion of its own volume,and repeated repair of solid electrolyte film（SEI）in the process of repeated charging and discharging.This results in the rapid attenuation of battery capacity,the decrease of coulomb efficiency,the shortening of cycle life and the short circuit of the battery.To solve the above problems,this paper designed a lithium-philic framework with multiple functions.With the help of the lithium-philic material evenly distributed on the surface and its own three-dimensional skeleton,the lithium anode was modified through a structured strategy,which delayed the growth of lithium dendrites and restrained the expansion of the lithium anode,thus achieving a lithium metal battery with excellent performance.The main research works are as follows:（1）Nickel foam（NF）was used as the base of the lithium-philic framework.The homogeneous copper particles were electroplated on the surface of nickel foam（to obtain the precursor of Cu@NF）,and then were selenized in situ.Finally,a lithium-philic framework modified with Cu1.8Se and NiSe2 selenides（Cu1.8Se-NiSe2@NF,CNSNF）.The two kinds of materials with different lithium-philic properties showed an alternating distribution pattern on nickel foam,so they had a better ability to induce lithium homogeneous nucleation and guide lithium homogeneous deposition in the process of lithium deposition.At the same time,the two selenides could also undergo cation exchange reaction with lithium metal to form Li2Se with excellent lithium ion conductivity in SEI film.These advantages enabled the CNSNF framework to show a 97.8%coulomb efficiency and stable 180 cycles（1 mA cm-2/1 mAh cm2）in a half battery performance test.The corresponding symmetric cell showed low polarization voltage and good cycle stability（1000 h）under the condition of current density of 1 mA cm-2 and cycle capacity of 5 mAh cm-2.In the C V test,high exchange current density was also shown.These results show that the electrochemical performance of half cells assembled by the CNSNF framework and corresponding symmetric cells was better than that of CNF and NF frameworks.（2）A lithiophilic framework（Cu3P-Ni2P@NF,CNPNF）rich in diphosphide was obtained by in-situ phosphating the precursor Cu@NF.The multi-particle spherical Cu3R and granular Ni2P on the CNPNF framework showed relatively uniform distribution,providing abundant deposition sites for lithium metal.These two phosphide and lithium was able to have cation exchange reaction,Forming Li3P with good conductivity of lithium-ion.Thus,the half-cell assembled from the CNPNF framework had a lower nucleation overpotential（14.9 mV）and showed a higher coulomb efficiency（98.3%）at deposition/stripping conditions of 1 mA cm2/l mAh cm-2,and stably cycled 280 times at multiple current densities and cycling capacities.There is still a relatively outstanding performance.The corresponding symmetric battery also shows excellent performance under the condition of current density and cycle capacity of 5 mA cm-2 and 5 mAh cm-2,respectively.At a low polarization voltage（70 mV）,it was stably cycled for 1800 h.Through these results,it can be found that the CNPNF framework modified lithium metal anode further widened the gap in electrochemical performance compared with CNF and NF framework,and was better than CNSNF framework,because of the higher binding energy of P element and Li element.（3）Press Cu_1.8Se-NiSe₂@NF（CNSNF）and Cu₃P-Ni₂P@NF（CNPNF）frameworks and lithium foil respectively to form corresponding anode.Expressed as Li-Cu1.8SeNiSe₂@NF（LCNSNF）and Li-Cu₃P-Ni₂P@NF（LCNPNF）,and matched with cathode materials LiFePO4 and NCM622,the complete battery was assembled,and the related electrochemical performance was tested.With LCNSNF as the anode and LFP（LiFePO4,11.5 mg cm-2）as the positive electrode,the full battery made 300 stable cycles at the charging ratio of 0.5 C（1 C=170 mAh g-1）,and the capacity retention rate reached 94.3%.In the case of multiple charge/discharge ratios and the battery assembled with NCM622,the performance improvement was obvious.When the LCNPNF anode was matched with the high-load positive electrode（LiFePO4,11.5 mg cm-2）,the resulting full battery underwent 400 stable cycles at 0.5 C charge/discharge ratio,and the capacity retention rate reached 88.0%.Under 5 C of charge/discharge rate,the cycle after 50 laps could still LED lights to the hand（consists of 29 diode）continuous light 20 min,and Li‖LFP battery compared with all the brightness of the more obvious gap.The lithium anode modified by CNSNF and CNPNF have a greater improvement in the application of whole batteries than that of pure lithium metal anode,indicating that both of these two lithiophilic frameworks have a good application prospect.