Electrochemical cycling behavior of LiFePO4 cathode charged with different upper voltage limits
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Keywords: Lithium ion batteries Lithium iron phosphate Charge voltage limit Capacity decay Lithium ion consumption
abstract
Electrochemical cycling behavior of LiFePO4 (LFP) cathode charged with different upper voltage limits has been studied. Reversible capacity of the cathode is not significantly increased by pushing up the charge voltage limit. However, charge voltage limit plays a role affecting the passivation film of the electrode. When cycled with low charge voltage limit, the passivation film is not well developed and the LFP electrode exhibits high surface impedance. When charged to extremely high voltage limit, oxidation of electrolyte produces carbon-based layer coating the LFP particles. The optimized charge voltage limits of 3.9 and 4.3 V are obtained under different experimental conditions. Long term cycling behavior of full cell is evaluated against MCMB anode. After 1000 electrochemical cycles, around 60% of the initial capacity is lost. Lithium inventory loss is found to be the main factor responsible for the cell failure. The impact of charge voltage limit on the cycling performance of LFP cathode is buried in the Li consumption during electrochemical cycles. Fe precipitation and the resultant impedance rise on the anode side, which are widely accepted to be responsible for the capacity decay of graphite/LFP full cells, is not observed in this study.
This paper presents the impact of charge voltage limits on the electrochemical behavior of both LFP half cell and LFP–MCMB full cell. The reversible capacity, rate capability and long-term cycling performance of the cells with different charge voltage limits were investigated. Optimized charge voltage limits of 3.9 and 4.3 V were obtained under different experimental conditions. The mechanism relating to the capacity decay of the full cells during long-term
a School of Energy, Soochow University, Suzhou, Jiangsu 215006, China b Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, CA 94720, USA
Electrochimica Acta 62 (2012) 256–262
Contents lists available at SciVerse ScienceDirect
Electrochimica Acta
journal homepage: /locate/electacta
Although LFP cathode has a very flat voltage profile at 3.4 V vs. Li/Li+, the charge voltage limits applied to the material varies from 3.7 to 4.6 V have been reported [9–12]. For many cathode materials, charge voltage limit significantly influences the cell capacity, energy, and cycleability. For example, an optimized charge voltage limit of 4.3 V was obtained for LiNi1/3Co1/3Mn1/3O2-MCMB full cell to attain both satisfactory energy density and cycle life [13]. The specific energy can be increased when the charge voltage limit is improved. Meanwhile, the cycling behavior is worsened due to the occurrence of more side reactions at the electrode/electrolyte interface including electrolyte oxidation and metal ion dissolution. There is no doubt that an optimum charge voltage limit helps to develop adequate testing protocols and design appropriate testing procedures for LFP-based cells. However, to the best of our knowledge, the effects of charge voltage limit on the electrochemical behavior of LFP-based half cell and full cell has not been reported.
0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2011.12.019
electrochemical cycles. The results are helpful for simulating and predicting the battery performance in PHEV or HEV scycling behavior of LiFePO4 cathode charged with different upper voltage limits
Honghe Zheng a,b,∗, Lili Chai a, Xiangyun Song b, Vince Battaglia b
∗ Corresponding author at: School of Energy, Soochow University, Suzhou 215006, China. Tel.: +86 512 69153523.
E-mail addresses: hhzheng66@, hhzheng@ (H. Zheng).
article info
Article history: Received 9 October 2011 Received in revised form 7 December 2011 Accepted 8 December 2011 Available online 16 December 2011
© 2011 Elsevier Ltd. All rights reserved.
1. Introduction
LiFePO4 (LFP) cathode has the advantages of high rate capability, high specific capacity (170 mAh g−1), good safety attribute, attractive cost competitiveness, and low toxicity. Its cell chemistry has been extensively studied and developed in the recent 10 years [1–4]. This material is widely accepted to be a safe and cost-effective cathode material with great promise for high energy PHEVs (plug-in hybrid electric vehicles) and high power HEVs (hybrid electric vehicles). Above all that, LFP operates at a benign voltage of 3.4 V and experiences a very limited change in lattice dimensions from fully lithiated to fully delithiated state. This endorses LFP cathode with excellent long-term cyclings. 1500–2000 cycles have been reported in laboratory tests for lithium ion cells based on LFP cathode [5–8]. However, for practical application in PHEV or HEV purposes, a cycle life of 5000 cycles with 80% DOD (depth of discharge) is required with a calendar life of around 15 years. To meet the aggressive requirements, there is still a lot of work to understand the cell chemistry and the capacity fade mechanisms during long-term
abstract
Electrochemical cycling behavior of LiFePO4 (LFP) cathode charged with different upper voltage limits has been studied. Reversible capacity of the cathode is not significantly increased by pushing up the charge voltage limit. However, charge voltage limit plays a role affecting the passivation film of the electrode. When cycled with low charge voltage limit, the passivation film is not well developed and the LFP electrode exhibits high surface impedance. When charged to extremely high voltage limit, oxidation of electrolyte produces carbon-based layer coating the LFP particles. The optimized charge voltage limits of 3.9 and 4.3 V are obtained under different experimental conditions. Long term cycling behavior of full cell is evaluated against MCMB anode. After 1000 electrochemical cycles, around 60% of the initial capacity is lost. Lithium inventory loss is found to be the main factor responsible for the cell failure. The impact of charge voltage limit on the cycling performance of LFP cathode is buried in the Li consumption during electrochemical cycles. Fe precipitation and the resultant impedance rise on the anode side, which are widely accepted to be responsible for the capacity decay of graphite/LFP full cells, is not observed in this study.
This paper presents the impact of charge voltage limits on the electrochemical behavior of both LFP half cell and LFP–MCMB full cell. The reversible capacity, rate capability and long-term cycling performance of the cells with different charge voltage limits were investigated. Optimized charge voltage limits of 3.9 and 4.3 V were obtained under different experimental conditions. The mechanism relating to the capacity decay of the full cells during long-term
a School of Energy, Soochow University, Suzhou, Jiangsu 215006, China b Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, CA 94720, USA
Electrochimica Acta 62 (2012) 256–262
Contents lists available at SciVerse ScienceDirect
Electrochimica Acta
journal homepage: /locate/electacta
Although LFP cathode has a very flat voltage profile at 3.4 V vs. Li/Li+, the charge voltage limits applied to the material varies from 3.7 to 4.6 V have been reported [9–12]. For many cathode materials, charge voltage limit significantly influences the cell capacity, energy, and cycleability. For example, an optimized charge voltage limit of 4.3 V was obtained for LiNi1/3Co1/3Mn1/3O2-MCMB full cell to attain both satisfactory energy density and cycle life [13]. The specific energy can be increased when the charge voltage limit is improved. Meanwhile, the cycling behavior is worsened due to the occurrence of more side reactions at the electrode/electrolyte interface including electrolyte oxidation and metal ion dissolution. There is no doubt that an optimum charge voltage limit helps to develop adequate testing protocols and design appropriate testing procedures for LFP-based cells. However, to the best of our knowledge, the effects of charge voltage limit on the electrochemical behavior of LFP-based half cell and full cell has not been reported.
0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2011.12.019
electrochemical cycles. The results are helpful for simulating and predicting the battery performance in PHEV or HEV scycling behavior of LiFePO4 cathode charged with different upper voltage limits
Honghe Zheng a,b,∗, Lili Chai a, Xiangyun Song b, Vince Battaglia b
∗ Corresponding author at: School of Energy, Soochow University, Suzhou 215006, China. Tel.: +86 512 69153523.
E-mail addresses: hhzheng66@, hhzheng@ (H. Zheng).
article info
Article history: Received 9 October 2011 Received in revised form 7 December 2011 Accepted 8 December 2011 Available online 16 December 2011
© 2011 Elsevier Ltd. All rights reserved.
1. Introduction
LiFePO4 (LFP) cathode has the advantages of high rate capability, high specific capacity (170 mAh g−1), good safety attribute, attractive cost competitiveness, and low toxicity. Its cell chemistry has been extensively studied and developed in the recent 10 years [1–4]. This material is widely accepted to be a safe and cost-effective cathode material with great promise for high energy PHEVs (plug-in hybrid electric vehicles) and high power HEVs (hybrid electric vehicles). Above all that, LFP operates at a benign voltage of 3.4 V and experiences a very limited change in lattice dimensions from fully lithiated to fully delithiated state. This endorses LFP cathode with excellent long-term cyclings. 1500–2000 cycles have been reported in laboratory tests for lithium ion cells based on LFP cathode [5–8]. However, for practical application in PHEV or HEV purposes, a cycle life of 5000 cycles with 80% DOD (depth of discharge) is required with a calendar life of around 15 years. To meet the aggressive requirements, there is still a lot of work to understand the cell chemistry and the capacity fade mechanisms during long-term