Investigation On Improvement Of Long Cycle Performance Of Lithium Manganate-Zinc Aqueous Battery Under High Current Density

Lithium-ion batteries are widely used in today’s society,the current lithium-ion batteries mainly use organic electrolytic liquid system,and the organic electrolyte is toxic and flammable,there are safety risks and not enough environmental protection,aqueous lithium-ion batteries because of its high safety,good environmental protection,lower cost advantages,began to get a lot of attention.Spinel lithium manganate has been widely researched as a cathode material for lithium-ion batteries because of its advantages of large reserves,simple production process,low cost and non-toxic and pollution-free.Zinc negative electrode has stable potential and large theoretical specific capacity,and is also a commonly used cathode material for ion batteries.Mixed-ion batteries attract the attention of researchers because both conductive ions can participate in the electrochemical reaction process of the battery,thereby improving the overall utilization rate of aqueous lithium-ion batteries.Based on the above advantages,this paper uses commercial lithium manganate as the positive electrode material,zinc sheet as the negative electrode,and the electrolyte uses 1 mol/L Li₂SO₄and 1 mol/L Zn SO₄mixed aqueous solution to assemble the lithium-zinc hybrid ion battery.The purpose of this paper is to make the battery of this system have relatively excellent long cycle performance under high current density.The research method used is to improve the battery system by improving some parameters during battery assembly and adding additives to the electrolyte,etc.The main research results and relevant conclusions obtained are as follows:（1）Battery assembly test,and improve battery performance by improving battery parameters.When the mass ratio of each substance is selected during the preparation of the positive electrode plate of the battery,the active substance commercial lithium manganate∶conductive agent acetylene black∶binder PVDF=7∶2∶1 is better than that when it is 8∶1∶1,which can effectively reduce the internal resistance of the battery cycle.The charge and discharge range of 1.2-2.0V is better than that of 1.5-2.0V,so that the battery can have a better coulomb efficiency,which can be stabilized at about 97%.The specific capacity of the battery decreases very fast when the current density is 740 m A/g,and the attenuation rate is significantly slowed down after a certain amount of manganese sulfate is added,but the appropriate concentration of manganese sulfate is related to the quality of the active substance in the positive electrode of the battery.（2）The appropriate mass range of active material and the concentration of added manganese sulfate were determined by contrast experiment.The active material mass of the positive electrode plates prepared in the experiment was roughly divided into mass range 1（below 2 mg）,mass range 2（2-4 mg）,and mass range 3（4-6 mg）.On the premise of not adding manganese sulfate to the electrolyte,the batteries in these three mass ranges are cycled under the current density of 740 m A/g,500 m A/g,300 m A/g and 100 m A/g,and the method of controlling the equal cycle time of a single cycle by adjusting the current density is adopted.The results show that the battery with a mass range of 3（4-6 mg）has the best discharge specific capacity retention rate after cycling,and it is used in subsequent batteries.On the basis of mass range 3,manganese sulfate was added to the electrolyte so that the concentrations of manganese sulfate in the electrolyte after addition were 0.03 mol/L,0.05mol/L,0.07 mol/L and 0.09 mol/L,respectively.By comparing the discharge specific capacity retention rate of the battery after 1000 cycles at 740 m A/g current density,it was found that the battery cycle performance was the best when the concentration of manganese sulfate was0.05 mol/L.（3）Select the appropriate electrolyte additive,and the long cycle performance of the battery at high current density is obviously improved by adding the additive.Under the premise of mass range 3 and adding 0.05 mol/L manganese sulfate,the surfactant fatty acid methyl ester ethoxylate FMEE was added to the battery,and the cycle stability became better.When the concentration of FMEE is 0.005 wt%,the battery has a discharge specific capacity of 71.9 m Ah/g after 1000 cycles at 740 m A/g current density,and the capacity retention rate is 60.62%,while the battery without FMEE is only 27.28%,which is an increase of more than30%.Also,under the premise of mass range 3 and addition of 0.05 mol/L manganese sulfate,tetraethyl ammonium bromide TEAB was added to the battery.When TEAB concentration was 0.01 mol/L,the specific capacity of the battery decreased slightly at first and then increased.The specific discharge capacity of 101 m Ah/g after 1000 cycles at 740 m A/g current density is 100%,while the capacity retention rate of the battery without TEAB in the same group is only 34.36%,compared with an increase of more than 60%.