Summary

シンクロトロンベースのハードX線マイクロトモグラフィーを用いて電池の故障解析

Published: August 26, 2015
doi:

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 Additionally, breakage of active particles in the cathode and poor adhesion within the battery can cause cell failure.10

Many modes of battery failure occur on the micrometer scale. However, most battery materials are air sensitive making sample preparation for analysis by electron microscopy and traditional optical microscopy difficult. Synchrotron hard X-ray microtomography allows one to visualize the interior of a battery without disassembly.11-14 Furthermore, the technique produces a three-dimensional (3D) reconstruction of the assembled cell making it easy to find locations of failure.15 Finding robust techniques that enable researchers to develop the scientific understanding required to accurately predict the lifetime of a battery is critical for the design of next generation battery technologies. The procedure discussed herein will specifically demonstrate how one can prepare and image model batteries to study the growth of lithium metal dendrites through solid polymer electrolyte membranes.

Computed tomography (CT) scanning is not a new technique and has been used frequently for failure analysis in industry. Synchrotron-based X-ray microtomography is advantageous because the high brightness and flux of the source allow collection of images with high resolution and good signal to noise in a much shorter amount of time.16 Additionally, one can take advantage of the X-ray energy resolution to image at energies around a chemical species’ absorption edge, causing the components containing that chemical species to be identified.17 It was found that the synchrotron source provides sufficient flux to achieve good contrast between lithium metal and solid polymer electrolyte membranes enabling one to image lithium metal dendrites.15

The study discussed herein uses a high modulus, block copolymer electrolyte membrane.18 These high modulus membranes suppress lithium dendrite growth, lengthening the lifetime of batteries.19,20 However, dendrites still eventually puncture the membrane causing the battery to fail by short-circuit. It is important to understand the nature of dendrite formation and growth in these high modulus electrolyte membranes in order to design strategies to prevent their growth.

Protocol

1.電解質の準備 260キロ/モルのポリ(スチレン) – – ブロック -ポリ(エチレンオキシド)コポリマー(SEO)アニオン重合を使用して240キロ/モルを合成します。 水と酸素レベルが制御されているアルゴングローブボックス内のすべての追加のサンプル調製を行い、残る<5 ppmです。 乾燥したリチウムビス(トリフルオロメタン)スルホンイミド(LiTFSIを)塩と無水N…

Representative Results

上記の対称性のリチウムリチウム電池を90℃で循環している場合、電圧応答は 、図1に示すようになります。最終的には、リチウムデンドライトが電解質を通って成長し、セルが短絡することにより失敗します。このとき、図2に示したものは、短絡によって故障したサンプルに表示されますように、印加電流に対する電圧応答は、0.00 Vの樹状突起にまで低下します。?…

Discussion

X線は大気に触れることなく、試料の容易なイメージングを可能にする、保護ポーチ材料を貫通することができますので、硬X線マイクロトモグラフィーは、多くの電気化学的に活性な物質のような空気に敏感なサンプルに特に適しています。おそらく、このイメージング技術の最も貴重な特徴は、貫通したX線は、ユーザーがそれを破壊することなく、試料の内部を見るために可能にすること…

Divulgations

The authors have nothing to disclose.

Acknowledgements

Primary funding for the work was provided by the Electron Microscopy of Soft Matter Program from the Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The battery assembly portion of the project was supported by the BATT program from the Vehicle Technologies program, through the Office of Energy Efficiency and Renewable Energy under U.S. DOE Contract DE-AC02-05CH11231. Hard X-ray microtomography experiments were performed at the Advanced Light Source which is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Katherine J. Harry was supported by a National Science Foundation Graduate Research Fellowship.

Materials

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

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Harry, K. J., Parkinson, D. Y., Balsara, N. P. Failure Analysis of Batteries Using Synchrotron-based Hard X-ray Microtomography. J. Vis. Exp. (102), e53021, doi:10.3791/53021 (2015).

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