Decrease in Capacity in Mn-Based/Graphite Commercial Lithium-Ion Batteries

Abstract

A precise and simple temperature measurement technique during charge and discharge is applied to 5 Ah Al-laminated lithium-ion batteries (LiMn 2 O 4 /LiNi 0.8 Co 0.15 Al 0.05 O 2 cathode and graphite anode) using a quasi-adiabatic cell holder. The obtained temperature profiles are described in terms of the reactions of the anode and cathode. This technique is applied to a cycled cell, and the capacity fading mechanism is also indicated by the temperature profiles. From the comparison between the cell temperature profiles and the reaction heat flows of the half cells in each electrode obtained by an isothermal microcalorimeter, we find that the capacity fading of the cycled cell can be derived from the capacity fading of the cathode and also from the upward shift in the operated state of charge (SOC) of the cathode in the cell. The latter shift is derived from the irreversible loss of lithium at the anode, and it leads to the misalignment of the cathode and anode operation windows. The proposed temperature measurement technique has the potential to be applied to various types of large lithium-ion batteries during operation, thus providing a new approach to analyzing the degradation of lithium-ion batteries.The applications of lithium-ion batteries are now being extended from mobile use to hybrid, plug-in hybrid, and electric vehicles, and various stationary uses. In these systems, the lithium-ion batteries are required to have a larger capacity and a longer lifetime than those for mobile use. Determination of the degradation factor in cells is becoming essential for improving the lifetime of batteries. Postanalysis, such as analysis of the electrode structure, electrolyte composition, and solid electrolyte interface (SEI), is a conventional tool used to determine the degradation of materials in cells. However, a large number of samples are needed to determine the degradation process during the operation. Nondestructive analyzes, such as capacity retention, power fading, and AC impedance analysis, are other approaches to determining the degradation process during cell operation. However, using these approaches it is not easy to find a convincing relationship between capacity fading and the degradation of the materials and/or misalignment of the electrode-capacity window in the cathode and anode materials in a cell.Electrochemical calorimetry is a useful nondestructive approach to determining electrode reactions during the charge and discharge of lithium-ion cells. [1][2][3][4][5] This approach enables the reactions at each electrode to be separated by comparing the heat flow profiles of half cells. We previously reported its application to prismatic [graphite/LiMn 2 O 4 ] 2 and cylindrical 18650-type [graphite/LiCoO 2 ] 5 cells, determination of the thermal behavior of graphite and LiCoO 2 , and analysis of the degradation from heat flow profiles. However, the conductive-type microcalorimeter that was used had a size limitation (<50 mmφ), meaning that we could not apply it to larger cells. Therefore, a more versati...

Mechanism of Silicon Electrode Aging upon Cycling in Full Lithium‐Ion Batteries

“…Such an internal cell imbalance, as defined by Christensen and Newman and Harlow et al . and observed in the case of LiMn 2 O 4 /graphite, LiNi 0.8 Co 0.15 Al 0.05 O 2 /graphite, and Li 4 Ti 5 O 12 /LiFePO 4 Li‐ion postmortem studies results in a progressive shift in the electrode capacity ranges with respect to each other (marked by red arrows and resulting in different values of y and y ′ in Figure ). It is nevertheless the first time to our knowledge that such behavior is evidenced in the case of silicon electrodes.…”

Why do batteries fail?

“…Testing of aged electrodes in newly assembled cells (51) coupled to postmortem studies to probe any battery component sampled from distributed cell/electrode locations can provide critical information, especially if a wide spectrum of complementary experimental techniques is used (elemental analysis, optical and electron microscopy, diffraction, nuclear magnetic resonance, infrared, Raman, x-ray photoelectron spectroscopy, etc.) (52)(53)(54)(55)(56).…”

Degradation mechanisms of C6/LiNi0.5Mn0.3Co0.2O2 Li-ion batteries unraveled by non-destructive and post-mortem methods

“…Graphite is commonly used as anode in most Li-ion batteries due to the excellent cycling performance, high safety and considerable specific capacity. Generally, Li immobilization in the Solid-Electrolyte-Interface (SEI) layers is considered to be the main degradation mechanism at graphite electrodes [8][9][10][11][12][13]. The SEI growth consumes cyclable Li ions, leading to irreversible capacity losses.…”