Electrochimica Acta 111 (2013) 802–808
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Electrochimica
Acta
j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /e l e c t a c t
a
Capacity loss induced by lithium deposition at graphite anode for LiFePO 4/graphite cell cycling at different temperatures
Li Tan a ,Li Zhang a ,Qingna Sun a ,Ming Shen b ,Qunting Qu a ,∗,Honghe Zheng a ,∗
a School of Energy,Soochow University,Suzhou,Jiangsu 215006,China b
Huasheng Chemical Corporation,Zhangjiagang,Jiangsu 215635,China
a r t i c l e
i n f o
Article history:
Received 8July 2013
Received in revised form 14August 2013Accepted 14August 2013Available online xxx
Keywords:
Lithium ion batteries LiFePO 4cathode Capacity fade Lithium loss
Solid electrolyte interphase (SEI)
a b s t r a c t
Capacity fading of a commercial 18650LiFePO 4/graphite cell was investigated at different temperatures (25,40,50and 60◦C)until 30%of its capacity was lost.Capacity decrease of the cell is in linear relationship with cycle number and the slope of the capacity-fading line is increased by elevating temperature.The capacity-fade mechanisms were investigated by using a combination of electrochemical,structural and inductively coupled plasma (ICP)techniques.Lithium inventory loss was found to be the main cause for the capacity loss.At the end of the cycling test,the amount of lithium precipitated on the graphite anode surface was determined.Most of the consumed lithium is found on the graphite anode,especially at high temperature condition,illustrating that the majority of lithium loss was ascribed to the side reactions at the graphite anode/electrolyte interface.Fe deposition at the graphite anode surface aroused from its dissolution into the electrolyte is not significant even when the cell is cycled at 50◦C condition.
© 2013 Elsevier Ltd. All rights reserved.
1.Introduction
Lithium ion batteries have attracted world-wide attention since the first one was made by SONY company.LiFePO 4(LFP)cathode material,which was first reported by Goodenough et al.[1],is an important category of lithium ion battery cathode materials as it has the advantages of high rate capability,high specific capacity (170mAh g −1),good safety attribute,attractive cost competitive-ness,and low toxicity.This cell chemistry has been extensively studied and successively commercialized in the recent 10years.This cathode material experiences very small change in lattice dimensions from fully lithiated to fully delithiated state,which endorses the LFP with excellent long-term cycling property.There-fore,Li-ion batteries based on LFP cathode are widely accepted of great promise for high energy PHEVs (plug-in hybrid electric vehi-cles)and high power HEVs (hybrid electric vehicles)[2,3].However,capacity fading of LFP-based cells is still a severe problem for its practical application in PHEV or HEV purposes as the service life is still far from the aggressive requirements of 5000electrochemi-cal cycles with 80%DOD (depth of discharge)and a calendar life of 10–15years.
As for the aging mechanisms of LFP-based cells,four differ-ent causes have been reported [4–7]:(i)Structural damage of the
∗Corresponding authors.
E-mail addresses:qtqu@ (Q.Qu),hhzheng@ (H.Zheng).
active material,specifically,phase transition and/or structural dis-order of the crystallinite after long-term cycles.(ii)Impedance rise associated with the resistance growth at the electrode/electrolyte interface and/or due to the loss of electrical contact between active material particles.(iii)Loss of active materials resulted from the dissolution of transition cations into electrolyte and/or particle isolation from the bulk electrode.(iv)Lithium inven-tory loss resulted from side reactions at electrode/electrolyte interface relating to solid electrode interphase (SEI)growth and rearrangement.
In recent years,most of the research studies have shown that the consumption of cycleable Li due to side reactions within the cell is the main cause responsible for the capacity fade of LFP-based Li-ion cells.Strieble et al.[8,9]tested the cycled graphite anode and LFP cathode of a cycled LFP/graphite cell.They found that both the electrodes well maintained their specific capacity except the loss of lithium inventory.Dubarry et al.[10]attempted to identify the con-tributions of several factors to capacity loss by using an incremental capacity analysis.Again,lithium inventory loss is found to be the main cause of the capacity degradation of the LFP-based cell.Liu et al.[11,12]investigated the discharge profiles using a differential analysis and they confirmed that the loss of reversible Li is responsi-ble for most of capacity fade.They also used external lithium source to replenish the cycled cathode which has lost 30%of its capacity after 2730cycles.Most of the lost capacity was recovered and the cell cycled for additional 1500cycles.We investigated the electro-chemical cycling behavior of a LFP-based cell with different upper voltage limits and the results indicated that lithium inventory loss
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