Mesoscale-architecture-based crack evolution dictating cycling stability of advanced lithium ion batteries

doi:10.1016/j.nanoen.2020.105420

Nano Energy

Volume 79, January 2021, 105420

https://doi.org/10.1016/j.nanoen.2020.105420 Get rights and content

Highlights

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In situ AFM quantifies the anisotropic expansion/shrinkage of NMC primary particles.
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In situ XRD confirms the irreversible lattice and morphological changes induces microcracks.
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Prove that microcracks originate from core of polycrystalline NMC and extend to surfaces.
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Provide new insights on synthesis NMC with controllable crystalline architecture.

Abstract

The cracking phenomenon of Ni-rich NMC (LiNi_xMn_yCo_1−x−yO₂, x ≥ 0.6) secondary particles is frequently discovered and believed to be one of critical reasons deteriorating the long-term cycling stability of NMC cathode in lithium ion batteries (LIBs). However, the initiation and evolution of those cracks is still controversial due to the limited quantification especially by in situ monitoring, leading to the challenge of identifying an efficient approach to inhibit the formation of the fractures during repeated cycling. Herein, the irreversible, anisotropic cycling lattice and mesoscale expansion/shrinkage of nano-grains during the first cycle, as revealed by in situ X-ray diffraction (XRD) and in situ atomic force microscopy (AFM), have been quantified and confirmed to be the dominant driving forces of microcracks initiation at the grain boundaries. These microcracks preferentially nucleate at the core region with random oriented nano-grains in early stage. The further growth and aggregation of microcracks into macrocrack eventually results in microfracture propagation radially outward to the periphery region with more uniform nano-grain orientation. This mesoscale nano-grain architecture controlled cracking process highlights the importance of predictive synthesis of cathode materials with controllable multiscale crystalline architecture for high-performance LIBs.

Graphical Abstract

Introduction

Ni-rich NMC (LiNi_xMn_yCo_1−x–yO₂, x ≥ 0.6) is regarded as one of the most promising cathodes for next-generation lithium ion batteries (LIBs) because of its low cost and high energy. However, challenges exist in large-scale deployment of Ni-rich NMC due to its long-term cycling stability [1], [2] moisture sensitivity [3], [4] and gas generation after extensive cycling [5], [6]. Capacity degradation can be caused by different reasons, such as side reaction [7], cation mixing [8], dissolution of transition metal cations [9]. Moreover, particle cracking is generally observed during cycling and believed to be an important reason for Ni-rich cathode deterioration, which disconnects primary particles and promotes the occurrence of the above attenuation factors by the newly formed surface [10], [11], [12], [13].

More specifically, two distinctive kinds of cracks have been observed in Ni-rich NMC: the intergranular cracks and the intragranular cracks. Compared with the intragranular cracks, intergranular cracks are more prone to form during charge/discharge cycling [14]. Intergranular cracks not only induce high impedance and inhibit electrochemical reaction due to the weakening connections between nano-grains, but also create space for electrolyte to penetrate through particles, leading to accelerated surface side reactions and unwanted phase transformation [10], [13], [15], [16], [17]. It is generally acknowledged that the formation of intergranular cracks in Ni-rich NMC is due to anisotropic volume change upon delithiation and lithiation. As the cut-off potential of the cathode increases, this anisotropic volume change becomes more pronounced [18], [19]. However, the mechanistic understanding of NMC cathode failure is still ambiguous due to the lack of direct monitoring and quantification of the structural and morphological changes of NMC particles, especially under the working conditions.

In the present work, for the first time, we employ in situ atomic force microscopy (AFM), in situ X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) to probe the atomic to mesoscale structure evolution during cycling NMC cathode. The irreversible lattice and mesoscale size change of nano-grains during the first cycle is quantified and regarded to be the dominant driving force of forming microcracks at the nanosized grain boundaries in the core region. The further growth of microcracks into macrocrack eventually results in microfractures propagation from center to the surfaces of NMC secondary particles.

Section snippets

Material preparation

Ni_0.76Mn_0.14Co_0.10(OH)₂ precursor was synthesized using a mixed hydroxide co-precipitation method with NiSO₄·6H₂O, MnSO₄·H₂O and CoSO₄·7H₂O as start materials. The whole reaction happens in a continuously stirred tank reactor (CSTR) under N₂ atmosphere. The mixed solution with a concentration of 2 mol/L was continuously fed into the CSTR filled with 1.5 L distilled water. Meanwhile, 4 mol/L NaOH solution as precipitator and 10 mol/L NH₄OH solution as chelating agent were pumped into the CTSR.

Results and discussions

In situ AFM was applied to probe the cathode interface evolution under the electrical field in a working electrochemical cell. The mesoscale topography information was collected during the electrochemical processes. Since AFM does not require vacuum to operate, it offers advantages in studying the multiple scale structural change of cathode material during lithiation/delithiation in electrolyte solution. Fig. 1a depicts the schematic illustration of the liquid cell used for in situ AFM

Conclusions

The origin of “cracking” phenomenon in Ni-rich NMC secondary particles has been correlated to the nucleation and growth of microcrack during cycling. It has been discovered that the lattice volume change of each primary NMC particle, although minor during each cycle, gradually accumulates during multiple cycles, which leads to the formation of microcracks along grain boundaries between different primary particles. Especially in the core region, the primary particles are less oriented with each

CRediT authorship contribution statement

Jiangtao Hu: Conceptualization, Investigation, Writing - Original Draft. Linze Li: Investigation. Enyuan Hu: Formal analysis. Sujong Chae: Investigation. Hao Jia: Investigation. Tongchao Liu: Investigation. Bingbin Wu: Investigation. Yujing Bi: Investigation. Khalil Amine: Investigation. Chongmin Wang: Investigation. Jiguang Zhang: Investigation. Jinhui Tao: Methodology, Writing - Review & Editing. Jie Xiao: Conceptualization, Investigation, Writing - Review & Editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

This research was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy through Applied Battery Research Program. J. T. acknowledges the support of in situ AFM experiments and data analysis from U. S. Department of Energy under Award KC020105-FWP12152. PNNL is a multiprogram national laboratory operated by Battelle for the DOE under Contract DE-AC05-76RL01830. E. Hu at Brookhaven National Laboratory (BNL)

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View full text

Mesoscale-architecture-based crack evolution dictating cycling stability of advanced lithium ion batteries

Highlights

Abstract

Graphical Abstract

Introduction

Section snippets

Material preparation

Results and discussions

Conclusions

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgment

Front. Energy Res.

J. Power Sources

Mater. Today

Prog. Mater. Sci.

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Nat. Energy

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J. Electrochem. Soc.

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Nano Lett.

Storage characteristics of LiNi_0.8Co_0.1+xMn_0.1−xO₂ (x=0, 0.03, and 0.06) cathode materials for lithium batteries

Capacity fading of Ni-rich Li[Ni_xCo_yMn_1–x–y]O₂(0.6 ≤x≤ 0.95) cathodes for high-energy-density lithium-ion batteries: bulk or surface degradation