摘要
磷酸铁锂(LiFePO_(4),LFP)以低成本、高安全性、长循环寿命等优点在近些年来备受关注,然而市场上常见的LFP储能器件在0.1~2 C倍率的循环寿命为2000次左右。为了进一步开发高功率、长寿命的LFP储能器件,本文设计了容量为9 Ah的不同负极材料(硬碳/软碳/石墨)软包储能器件。对4 C大倍率循环性能进行探究,发现4000次循环后,硬碳和软碳用作负极的储能器件的容量保持率分别为83.0%、78.9%,优于石墨(51.6%)。通过XRD、EIS、容量增量法和电压微分法等手段进行分析,发现接触内阻和SEI膜内阻增加,以及结构变化造成负极中锂离子的消耗是容量衰减的主要原因。进一步探究石墨用作负极时循环寿命差的原因,发现石墨用作负极时库仑效率较低,工作温度较高,dQ/dV峰值在循环过程中发生更大的位移,峰强的降幅也较大。由于石墨的层间距为0.335 nm,小于软碳(0.360 nm)和硬碳(0.395 nm),在反复脱嵌锂过程中石墨更易发生结构变化,造成体积膨胀,因此循环后接触电阻和SEI膜电阻增长幅度较高,锂离子扩散动力学也更差。与石墨相比,硬碳和软碳用作大倍率LFP储能器件的负极活性物质时具有更长的循环寿命。
In recent years,LiFePO_(4)(LFP)has garnered significant attention because of its low cost,high safety,and long cycle life.However,conventional LFP energy storage devices typically have a cycle life of approximately 2000 cycles at a rate of 0.1-2 C.To further develop high-power and long-life LFP energy storage devices,pouch-type energy storage devices based on different anode materials(hard carbon/soft carbon/graphite)with a capacity of 9 Ah were designed.Examining the cycling performance at a high rate of 4 C revealed that after 4000 cycles,the capacity retentions of energy storage devices using hard and soft carbons as anodes were 83.0%and 78.9%,respectively,outperforming those using graphite,which had a retention of 51.6%.Analytical techniques such as XRD and EIS analyses,incremental capacity analysis,and different voltage analyses revealed that the primary causes of capacity fading include increased contact resistance,SEI film resistance,and lithium-ion consumption in the anode due to structural changes.Further investigation into the poor cycle life of graphite as an anode material revealed that graphite exhibits a lower Coulomb efficiency,higher operating temperature,greater displacement,and a decrease in peak intensity in the dQ/dV peak during cycling.The interlayer spacing of graphite was 0.335 nm,which is smaller than that of soft carbon(0.360 nm)and hard carbon(0.395 nm).Graphite is more susceptible to structural changes and volume expansion during repeated lithium removal and insertion processes.Thus,graphite exhibits higher contact resistance and SEI film resistance for lithium ions and poorer diffusion kinetics.Compared with graphite,hard and soft carbons exhibit longer cycle lives as anode-active materials in high-power LFP energy storage devices.
作者
张玉曼
范羚羚
杨重阳
ZHANG Yuman;FAN Lingling;YANG Chongyang(Shanghai Aowei Technology Development Co.Ltd.,National Engineering Research Center for Supercapacitor for Vechicles,Shanghai 201203,China)
出处
《储能科学与技术》
CAS
CSCD
北大核心
2024年第9期3245-3253,共9页
Energy Storage Science and Technology
关键词
磷酸铁锂
硬碳
软碳
石墨
循环寿命
LiFePO_(4)
hard carbon
soft carbon
graphite
cycle life
作者简介
第一作者:张玉曼(1997-),女,硕士,主要从事磷酸铁锂储能器件的研究,E-mail:jshfengwu@163.com;通信作者:杨重阳,副研究员,主要从事高能量高功率储能器件研究,E-mail:ycy6142@sina.com。
