A Study on the Cycle Life of Lithium-Ion Batteries Using In Situ⁷Li Solid-State Nuclear Magnetic Resonance

Abstract

The capacity fading of lithium ion batteries (LIBs) is investigated, using in situ 7 Li solid-state nuclear magnetic resonance (NMR). LIB cells consisting of graphite or hard carbon and LiCoO 2 are used and cycled under two different temperatures (10 and 25 • C) and charge current rates (0.5 and 1 C). The cell capacity and the amount of Li stored in carbon are measured with a battery cycler and in situ 7 Li solid-state NMR measurements before the beginning of the test and after every 100 test cycles. The in situ 7 Li solid state NMRs provide sufficient information throughout the cycle tests to characterize all test conditions. The cell capacities are analyzed in terms of the 7 Li NMR peak intensity, attributed to Li stored in carbon. This intensity shows affine proportionality with the cell capacity for every evaluation, with an additive constant that decreases with the increase in cell capacity fading. This may be related to the loss of Li storage caused by voltage "slippage. Lithium-ion batteries (LIBs) have been widely used in portable electronic devices and as power sources for mobile machines such as electric vehicles, hybrid electric vehicles, e-bikes, e-scooters, and electric wheelchairs. To ensure the sustainability and endurance of these devices, it is necessary to understand battery degradation (in both capacity and power) due to daily use.1 LIBs are charged and discharged by Li insertion without chemical reactions, and the degradation of electrode materials is consequently small. LIBs are therefore widely considered to be excellent batteries, with long cycle lives. However, capacity fading occurs when LIBs are used outside moderate temperature ranges, at high current, with high voltage storage, etc. The capacity balance between positive and negative electrodes is lost (called "slippage") because of charge and discharge operations with low accuracy controllers or parasitic reactions during operation and storage.2-9 Slippage causes gradual capacity fading, because cell capacity is determined by the capacity balance between the positive and negative electrodes.Previous studies have reported how and when slippage induces capacity fading, but not how slippage occurs and what it is exactly. To fully understand capacity fading and slippage, nondestructive measurements are needed, because capacity fading due to slippage will only be properly observed if the cell internal conditions are fully maintained.To examine the state inside the battery without destroying it, we developed an in situ 7 Li solid-state nuclear magnetic resonance (NMR) measurement method, using full-cell test equipment consisting of actual positive and negative electrodes. Using this method, we studied Li insertion/extraction in carbon with charge/discharge operations, Li dendrite growth during overcharges, and the properties of dendritic Li after being formed. 10,11 This study investigated the change in NMR peak intensity of the Li stored in the cycle test, to elucidate cell capacity fading in terms of the amount of Li storage at the select...

Study of Li Metal Deposition in Lithium Ion Battery during Low-Temperature Cycle Using In Situ Solid-State7Li Nuclear Magnetic Resonance

“…20 The NMR probe featured a genuine flattened solenoid coil tuned at the 7 Li Larmor frequency (116.41 MHz) to make sufficient space for the cell while still receiving an adequate signal. 18,19 The cell was placed in the coil, and its plane face was directed perpendicular to the magnetic field. The following NMR settings were used: single-pulse sequence, 6 μs pulse length, 1 s pulse delay, 90 • spin flip, 800 scans, and chemical shifts referenced to a saturated aqueous LiCl solution.…”

“…16 We developed an in-situ solid-state 7 Li NMR method using a small laminated full cell composed of actual electrodes to analyze the cell reaction without disassembling the cell. 18,19 The NMR method can be used to investigate the state of Li atoms regardless of whether they exist as ions in an electrolyte or they are stored in electrodes [especially in graphite negative electrode material as a graphite intercalation compound (GIC)]. The NMR method can also be used to investigate accidentally deposited Li metal.…”

Challenges in Developing Electrodes, Electrolytes, and Diagnostics Tools to Understand and Advance Sodium‐Ion Batteries

“…34,489 The local structural and dynamics can be obtained through the interactions of the nuclear spin with its local environment, including chemical shift and dipolar and quadrupolar interactions. [490][491][492][493] Together with electrochemical devices, solid-state NMR spectroscopy can track dynamic processes for both crystalline and amorphous electrode materials during the electrochemical process. 485,[494][495][496][497][498][499][500][501][502][503][504][505][506][507][508][509][510][511][512] Atoms with a nuclear spin I≠0 possess a magnetic moment and are, in principle, detectable by NMR spectroscopy.…”

Slow Stabilization of Si-Li Alloys Formed during Charge and Discharge of a Si-C Mixed Electrode Studied by In Situ Solid-State7Li Nuclear Magnetic Resonance Spectroscopy

“…19 The NMR probe featured a flattened solenoid coil tuned at the 7 Li Larmor frequency (116.41 MHz) to allow sufficient space for the cell and receive an adequate signal. [20][21][22] The cell was folded in the coil and its plane face was directed perpendicular to the magnetic field. The NMR settings were as follows: single pulse sequence, 6 μs pulse length, 1 s pulse delay, 90 • spin flip, 1000 scans, and chemical shifts referenced to a saturated aqueous LiCl solution.…”