Modification And Electrochemical Performance Of Alkali Metal Anodes

Using alkali metals as anodes in the batteries have unique advantages,such as higher theoretical specific capacity(3860 mAh g-1 of Li and 1166 mAh g-1 of Na)and lower electrochemical potential(Li is-3.04 V and Na is-2.71 V versus the standard hydrogen electrode),which has caused attention in the field of energy at home and abroad.However,a lot of problems occur because of the formation of Li and Na dendrite.For example,the dendrite is able to pierce the separator of batteries resulting in the safety problems,accelerate the side-reaction with the electrolyte,undermine stability of solid electrolyte interphase(SEI)and increase the impedance of batteries and so on.These tricky problems affect the practical applications of the alkali metal batteries.Therefore,exploring a method of suppressing dendrite has important theoretical significance and research value.To solve these above problems,the four kinds of protective layers are formed between the alkali metal anodes and separator in this work.Thus,the formation of dendrite is able to be suppressed,resulting in improved safety and electrochemical performance of alkali metal batteries.The main work is as follows:(1)Design of lithium metal anodes by interface modification and its electrochemical performance in the lithium metal batteries.At ambient temperature,a facile immersion method is used to realize the surface alloying process with barium.And the lithium metal is able to be modified by this method in order to suppress the formation of lithium dendrite.The Ba-Li protective layer,formed on the surface of lithium metal electrode,shows a quite good interfacial adhesion.By this Ba-Li protective layer,the diffusion barrier of lithium atom is significantly reduced on the surface of electrode,which promotes the uniform deposition and suppresses the formation of lithium dendrite.On the surface of Ba-modified lithium electrode,the dendrite is suppressed in commercial carbonate electrolyte.The cycling performance and rate capacity can be obviously improved in the modified lithium metal batteries.(2)Design of nano-sized Bi modified separator and its electrochemical performance in the lithium metal batteries.For the above method of interface modification,the content of water and oxide have to be below 0.01 ppm in the operating-environments.In order to push the process of industrialization,the separator modification is put forward to form the protective layer for modifying the lithium metal batteries.Lithiophilic Bi has the lower price than the Ba metal.Therefore,the prepared nano-sized Bi by the dealloying is used as the functional material of modifying the separator in the lithium metal batteries.The method of Bi-modified separator can not only achieve enhanced the wettability,but also suppress the formation of lithium dendrite.The lithium metal batteries with Bi-modified separator have much better cycling stability and rate capacity than the blank ones.(3)Design of Co3O4 nanosheets modified separator and its electrochemical performance in the lithium metal batteries.Continuing with the method of separator modification,in order to explore the suppression effect of different functional material on dendrite,Co3O4,which has different morphology from Bi,is selected as the functional material of modifying the separator.The new protective layer is able to be formed in order to modify the lithium metal batteries.After the Al is etched from the Al-10Co with the calcination,the Co3O4 nanosheets can be successfully prepared.And during this process,the morphology of Co3O4 nanosheets can be controlled by adjusting the dealloying parameter.Using lithiophilic Co3O4 nanosheets as the functional materials of modifying commercial PE separator contributed to uniform deposition and dendrite inhibition.The modified lithium metal symmetric and full batteries show superior electrochemical performance.(4)Design of Mg(Ⅱ)@Ti3C2 modified current collector and its electrochemical performance in the sodium metal batteries.Lithium material consumption is soaring.Taking long-term energy storage into consideration,the sodium metal batteries is worth investing.In view of these shortcomings of the commercial Cu current collector in the sodium metal anodes,the multi-functional Mg(II)@Ti3C2 is used as the protective layer of Cu foil.After modifying the sodium metal batteries with this functional material,the wettability between electrolyte and Cu foil is dramatically improved.Sodiophilic Mg(II)@Ti3C2 can reduce the nucleation barriers and promote the uniform deposition,thereby suppressing the formation of dendrite.The modified sodium metal batteries show much more excellent performance in all electrochemical tests including the symmetric cells,Na-Cu cells,and full cells.