Failure Analysis Batterijen met synchrotron gebaseerde Hard X-ray Microtomografie

Summary

Synchrotron-based hard X-ray microtomography is used to image the electrochemical growth of dendrites from a lithium metal electrode through a solid polymer electrolyte membrane.

Abstract

Imaging morphological changes that occur during the lifetime of rechargeable batteries is necessary to understand how these devices fail. Since the advent of lithium-ion batteries, researchers have known that the lithium metal anode has the highest theoretical energy density of any anode material. However, rechargeable batteries containing a lithium metal anode are not widely used in consumer products because the growth of lithium dendrites from the anode upon charging of the battery causes premature cell failure by short circuit. Lithium dendrites can also form in commercial lithium-ion batteries with graphite anodes if they are improperly charged. We demonstrate that lithium dendrite growth can be studied using synchrotron-based hard X-ray microtomography. This non-destructive imaging technique allows researchers to study the growth of lithium dendrites, in addition to other morphological changes inside batteries, and subsequently develop methods to extend battery life.

Introduction

Researchers are actively investigating battery chemistries with theoretical energy densities over an order of magnitude larger than traditional lithium-ion batteries.^1,2 These high-energy-density batteries will make electric vehicles more competitive with their gasoline-powered counterparts.³ However, these new chemistries have several failure modes that preclude their use in commercial technologies. For example, these battery chemistries require a lithium metal anode to achieve large enhancements in energy density; unfortunately, lithium metal is prone to dendrite growth as lithium ions are reduced at the anode surface during charging.^4-9

Protocol

1. Electrolyte Preparation

1. Synthesize a 240 kg/mol – 260 kg/mol poly(styrene) - block - poly(ethylene oxide) copolymer (SEO) using anionic polymerization.
   1. Perform all additional sample preparation in an Argon glovebox where the water and oxygen levels are controlled and remain <5 ppm.
   2. Dissolve 0.3 g of polymer in anhydrous N-methyl-2-pyrrolidone (NMP) with dry lithium bis(trifluoromethane)sulfonimide (LiTFSI) salt. Use a LiTFSI salt to SEO mass ratio of 0.275 and an NMP to SEO mass ratio of 13.13.
      Note: This quantity of polymer will yield a membrane large enough to make approximately 20 samples.
   3. ....

Results

When the symmetric lithium-lithium cells described above are cycled at 90 °C, the voltage response looks like that shown in Figure 1. Eventually, lithium dendrites will grow through the electrolyte and cause the cell to fail by short circuit. When this happens, the voltage response to the applied current will drop down to 0.00 V. Dendrites, like the one shown in Figure 2 appear in samples that have failed by short circuit. Non-electrolyte spanning dendrites are also found in the samples........

Discussion

Hard X-ray microtomography is especially well-suited for air-sensitive samples, like many electrochemically active materials, since the X-rays can penetrate through protective pouch material, enabling facile imaging of the sample without exposure to air. Perhaps the most valuable characteristic of this imaging technique is that the penetrating X-rays allow the user to see inside of the sample without destroying it. Most common imaging techniques, like scanning electron microscopy and traditional optical microscopy, can o.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Anhydrous N-methyl-2-pyrrolidone	MILLIPORE	MX1396-7
Lithium bis(trifluoromethane)sulfonamide	MILLIPORE	8438730010
Lithium metal	FMC Lithium	None	Lectro Max 100
Pouch material	MTI Corporation	EQ-alf-400-7.5M
Nickel tabs	MTI Corporation	EQ-PLiB-NTA3