LiFePO4 technical papers mega thread (ok mayby not so mega)

[evm1024]

There are a lot of technical papers and the like for LiFePO4 that I thought it would be nice to have a thread listing them.

With that in mind here are links to three papers.

[evm1024]

Failure Mechanism Investigation of Commercial LiFePO4*Cells in Different Operating Conditions


Failure Mechanism Investigation of Commercial LiFePO4 Cells in Different Operating Conditions
Yadong Liua, Qi Liua, Zhe-Fei Lib, Fan Yangb, Yang Renc, Wenquan Luc and Jian Xieb
+ Author Affiliations

aIndiana University Purdue University Indianapolis
bIndiana University-Purdue University Indianapolis
cArgonne National Laboratory
Abstract
The rapid growth of the Li-ion battery (LIB) market has greatly driven research on LIBs, particularly on LIB failure mechanisms under different operating conditions (long-term cycling, overcharge, over-discharge, high temperatures, low temperatures, etc.) due to safety issues1. Up to now, there are only very few of reports on the capacity fade mechanisms in the commercial batteries2. It is paramount of scientific and engineering importance to understand the microstructure evolution during normal cycle in the commercial cells. To our knowledge, in situ monitoring of microstructure evolution during the capacity fade process in either a commercial battery or lab-made batteries has never been reported before.

In this work, the capacity fade/failure processes of commercial 18650 LiFePO4 cell during the long term normal charge/discharge, overcharge, and over-discharge cycling was systematically investigated respectively. The commercial 18650 LiFePO4cells (A123 Systems) were chosen to be cycled for all cycling conditions until these cells reach 80% of initial capacity (typical criteria for EV application) or cannot be charged/discharged.

The cells were in situ characterized and the microstructure of the electrodes was investigated using synchrotron high-energy X-ray diffraction during long term normal cycling and overcharge/over-discharge cycling conditions. Synchrotron high-energy X-rays with photon energy of 115 KeV are capable of penetrate through thick samples, which allows us to probe commercial 18650 LiFePO4 cells without any cell modification and the results are presented herein. The result of 18650 cell after 2500 cycles is shown in Fig. 1. Our in situ experiment result show that loss of the active lithium source in the system is the primary cause of the capacity fade and the appearance of the inactive FePO4phase is proportional to the decrease of available lithium source during cycling.

Electrochemical Impedance Spectroscopy (EIS) is a powerful and quick analytical and diagnostic tool that can be used to study the internal resistance of Li-ion batteries during long-term normal cycling or overcharge/ over-discharge cycling3. The EIS results during overcharge and over-discharge process are shown in Fig. 2 and 3 respectively, and the de-convoluted Ohmic resistance, solid electrolyte interphase (SEI) resistance, and Warburg Coefficient, change with cycle number in some patterns, indicating the occurrence of corrosion of the current collector, SEI breakdown/decomposition and reformation, and the development of diffusion barriers of Li+ in the electrode, respectively. These parameters are associated with failure and can be used as indicators of incoming failure. Overall, EIS can be used as an effective and reliable tool to monitor the state of health, predict incoming failure of the LIB cells, and issue a warning before failure without disturbing the operation of the cells.

Figure 1

[evm1024]

Failure Investigation of LiFePO4 Cells under Overcharge Conditions


Failure Investigation of LiFePO4 Cells under Overcharge Conditions
Fan Xua, Hao Hea, YaDong Liua, Clif Dunb, Yang Renc, Qi Liua, Mei-xian Wanga and Jian Xiea,*,z
+ Author Affiliations

aDepartment of Mechanical Engineering, Purdue School of Engineering and Technology, Indiana University-Purdue University, Indianapolis, Indiana 46202, USA
bSchool of Dentistry, Indiana University, Indianapolis, Indiana 46202, USA
cX-Ray Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
Abstract
The failure mechanism of LiFePO4 cells during overcharge conditions has been systematically studied using commercial A123 18650 cells at a 1C rate and different conditions – from 5% to 20% overcharge (SOC = 105% to 120%). SEM/EDX, high-energy synchrotron XRD (HESXRD), and cyclic voltammetry (CV) were used to characterize the morphology, structure, and electrode potentials of cell components both in situ and ex situ. The failure behaviors for A123 18650 cells experiencing different degrees of overcharges were found to be similar, and the 10% overcharge process was analyzed as the representative example. The Fe redox potentials in the 1.2 M LiPF6 EC/EMC electrolyte were measured during the overcharge/discharge process using CV, proving that Fe oxidation and reduction in the cell during the overcharge/discharge cycle is theoretically possible. A possible failure mechanism is proposed: during the overcharging process, metallic Fe oxidized first to Fe2+, then to Fe3+ cations; next, these Fe2+ and Fe3+ cations diffused to the anode side from the cathode side; and finally, these Fe3+ cations reduced first to Fe2+ cations, and then reduced further, back to metallic Fe. During overcharge/discharge cycling, Fe dendrites continued growing from both the anode and the cathode sides simultaneously, penetrating through the separator and forming an iron bridge between the anode and cathode. The iron bridge caused micro-shorting and eventually led to the failure of the cell. During the overcharge/discharge cycles, the continued cell temperature increase at the end of overcharge is evidence of the micro-shorting.

[evm1024]

Failure Investigation of LiFePO4 Cells in Over-Discharge Conditions


Failure Investigation of LiFePO4 Cells in Over-Discharge Conditions
Hao Hea,d, Yadong Liua, Qi Liua, Zhefei Lia, Fan Xua, Clif Dunb, Yang Renc, Mei-xian Wanga and Jian Xiea,*,z
+ Author Affiliations

aDepartment of Mechanical Engineering, Purdue School of Engineering and Technology, Indiana University-Purdue University, Indianapolis, Indiana 46202, USA
bSchool of Dentistry, Indiana University, Indianapolis, Indiana 46202, USA
cX-ray Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
Abstract
The failure mechanism of LiFePO4 cells in over-discharge conditions has been systematically studied using commercial A123 18650 cells at a 1.0 C rate and different conditions – from 5% to 20% over-discharge (DOD = 105% to 120%). SEM/EDAX, high-energy synchrotron XRD (HESXRD), and cyclic voltammetry (CV) were used to characterize the morphology, structure, and electrode potentials of cell components both in situ and ex situ. The failure behaviors of A123 18650 cells experiencing different degrees of over-discharge were found to be similar, and the 20% over-discharge process was analyzed as the representative example. The Cu electrochemical potentials in the 1.2 M LiPF6 EC/EMC electrolyte were measured during the charge/over-discharge process using CV, proving that Cu oxidation and reduction in the cell during the charge/over-discharge cycle were theoretically possible to proceed. A possible failure mechanism is proposed: during the over-discharging process, Cu foil oxidized first to Cu+, then to Cu2+ cations; next, these Cu+ and Cu2+ cations diffused to the cathode side from the anode side; and finally, these Cu2+ cations reduced to Cu+ cations, and then reduced further, back to metallic Cu. During charge/over-discharge cycling, Cu dendrites continued growing from the cathode side, penetrating through the separator and forming a copper bridge between the anode and cathode. The copper bridge caused micro-shorting and eventually led to the failure of the cell. During the charge/over-discharge cycles, the continued cell temperature increase at the end of over-discharge is evidence of the micro-shorting.

Footnotes

[alansmith]

Thank u for the science. That was very informative.

[evm1024]

Originally Posted by alansmith

Thank u for the science. That was very informative.

You are welcome.

Hey all, Keep those papers coming to this thread. Feel free to post them here.

[evm1024]

Let's add in one more paper:

https://www.princeton.edu/~spikelab/papers/101.pdf

A comparison of lead-acid and lithium-based battery behavior
and capacity fade in off-grid renewable charging applications

abstract
The effects of variable charging rates and incomplete charging in off-grid renewable energy applications
are studied by comparing battery degradation rates and mechanisms in lead-acid, LCO (lithium cobalt
oxide), LCO-NMC (LCO-lithium nickel manganese cobalt oxide composite), and LFP (lithium iron
phosphate) cells charged with wind-based charging protocols. Poor pulse charge acceptance, particularly
for long pulses, contributes to incomplete charging and rapid degradation of lead-acid cells due to
apparent high rates of sulphation and resistance growth. Partial charging and pulse charging, common
lead-acid stressors in off-grid applications, are found to have little if any effect on degradation in the
lithium-based cells when compared to constant current charging. These cells all last much longer than
the lead-acid cells; the LFP batteries show the greatest longevity, with minimal capacity fade observed
after over 1000 cycles. Pulse charge acceptance is found to depend on pulse length in lead-acid and LFP
cells, but not in LCO and LCO-NMC cells. Excellent power performance and consistent voltage and power
behavior during cycling suggest that LFP batteries are well-suited to withstand the stresses associated
with off-grid renewable energy storage and have the potential to reduce system lifetime costs.

2013 Elsevier Ltd. All rights reserved.

[Nicholson58]

This is very educational

https://marinehowto.com/lifepo4-batteries-on-boats/