Research On Functional Carbon Additives To Improve Cycling Performance Of Battery And Its Mechanism

Environment and energy are the basis for human survival.At present,the world’s energy is still mainly dependent on fossil fuels.However,fossil fuels are increasingly depleted and cause environmental pollution,posing a threat to the sustainable development of mankind.Building an energy system dominated by new energy sources（such as wind energy and solar energy,etc.）is the only way for mankind to achieve sustainable development.However,new energy power generation is intermittent,and it is necessary to vigorously adopt energy storage systems to stabilize the volatility of new energy.Among various energy storage systems,battery energy storage has great advantages,among which lead-acid batteries（LAB）have the advantages of low cost,mature technology,strong safety,stability and reliability,and good resource reutilization.However,in new energy storage and transportation equipment systems,batteries often operate under high rate partial charge state（HRPSoC）,that is,large current pulse charging and discharging are performed in a partially charged state.Under HRPSoC conditions,the surface of the negative plate of the LAB is prone to pile up of Pb SO₄,leading to premature battery failure.Studies have shown that adding carbon materials to negative electrode active materials（NAMs）can effectively inhibit the accumulation of Pb SO₄ on the surface of the negative electrode and improve the HRPSoC performance of LAB.However,the concentration of added carbon materials in NAMs is often greater than 1 wt%,increasing The cost of LAB.More importantly,the addition of high-concentration carbon materials will change the physical properties of NAMs,such as apparent density and penetration,forcing LAB manufacturers to adjust the NAMs formula or negative plate manufacturing process,which limits the technology’s use Promotion of the LAB industry.In this paper,on the basis of not changing the traditional formula of NAMs,trace amounts of carbon materials are added to NAMs in a very simple way,which greatly improves the HRPSoC cycle life of LAB.The main research contents and results are as follows:1.The multi-walled carbon nanometers（MWCNTs）are acid-treated to obtain acid- treated MWCNTs（a-MWCNTs）.By incorporating trace amounts of a- MWCNTs into the traditional negative electrode paste of LABs,the study found that the chemical reaction that occurs during the curing process can be significantly affected through inducing the dominoes during the formation process because of MWCNTs contains rich oxygen containing groups which can make domino-shaped Pb flakes grown.These domino Pb tablets are quasi-rod- shaped and cross-linked with each other.The quasi-rod structure of the Pb sheet provides a channel for the rapid transfer of electrons,and the pores between the cross-linked Pb rods are conducive to the diffusion of the electrolyte,which greatly promotes the electrochemical reaction between Pb and Pb SO₄,and inhibits the hindrance of Pb SO₄ crystals.The accumulation of ions,thereby inhibiting the sulfation of the negative plate.The electrochemical test results show that under the condition of HRPSoC,the simulated battery with 100 ppm a-MWCNTs achieves 32010 cycles of HRPSoC,and the number of cycles is more than 1.5 times higher than that of the battery without a-MWCNTs.2.MWCNTs modified with cetyltrimethyl ammonium bromide（CTAB）to produce CTAB-MWCNTs were used as the carbon additive for NAMs to improve the cyclic performance of HRPSoC in LABs.CTAB is a cationic surfactant,which can functionally modify MWCNTs through non-covalent reactions and functionalizes them on the surface of MWCNTs.Incorporating this CTAB- MWCNTs into NAMs,the quaternary ammonium salt group（（CH₃）₃N⁺）on the surface can combine with Pb²⁺,forming crystals which have similar crystalline structure to Pb SO₄ and thereby increasing the content of 3BS in the cured NAMs.The experimental results show that in the cured NAMs with 100 ppm CTAB-MWCNTs,the 3BS percentage is as high as 26.21%,which is much higher than the negative plate with a-MWCNTs added in our previous study. Trace amounts of CTAB-MWCNTs have a great influence on the morphology of NAMs after formation:when the amount of CTAB-MWCNTs is 100 ppm,the NAMs after formation are composed of intersecting rod-shaped Pb.This structure can increase the porosity and ratio of NAMs.In addition,the one- dimensional structure of the Pb rod can provide a channel for the rapid transfer of electrons.Therefore,the electrochemical reaction between Pb and Pb SO₄ is accelerated,thereby effectively delaying the accumulation of Pb SO₄ crystals. The HRPSoC cycle life of the simulated battery was increased from 18012 cycles to 36496 cycles,which exceeded the HRPSoC performance of the simulated battery assembled from the negative plate doped with 100 ppm a- MWCNTs.3.Sodium dodecyl sulfonate（SDS）was modified on the surface of MWCNTs to obtain SDS-modified MWCNTs.A trace amount of SDS-MWCNTs is used as an additive to NAMs and added to the traditional negative electrode paste to make LAB negative electrodes.Studies have found that during the curing process of the negative electrode,the sulfonic acid groups on SDS-MWCNTs can combine with Pb²⁺ions to form Pb SO₄,which is beneficial to the formation of 3BS during the curing process,and greatly increases the content and size of 3BS in the cured NAMs.After formation,NAMs containing SDS-MWCNTs showed the morphology of interconnected lead rods.The one-dimensional structure of the lead rods provides a channel for long-range electron transfer, and the gaps between the lead rods and the holes on the lead rods are conducive to the diffusion of sulfuric acid,which accelerates the electrochemical reaction between Pb and Pb SO₄,and realizes the Pb SO₄ crystal Inhibition of aggregation. Experimental results show that the HRPSoC cycle life of a simulated battery assembled with a negative plate with 100 ppm SDS-MWCNTs can reach 45,692 cycles,which is more than 2.14 times the life of a simulated battery without SDS-MWCNTs.