Elsevier

Energy Storage Materials

Volume 27, May 2020, Pages 198-204
Energy Storage Materials

Suppressed dendrite formation realized by selective Li deposition in all-solid-state lithium batteries

https://doi.org/10.1016/j.ensm.2020.01.031Get rights and content

Abstract

Solid polymer electrolytes (SPEs)-based all-solid-state lithium batteries (ASSLBs) with high-safety and high-performance have been regarded as promising next-generation energy storage devices. A fly in the ointment is that the cycling life is significantly limited by the Li dendrite growth. To tackle the Li dendrite issue, a selective Li deposition strategy is proposed, for the first time, to suppress Li dendrite formation via the rational design of a patterned Li anode. Through a facile and low-cost template-press method, the Li anode was divided into numerous square Li with deep grooves around 100 ​μm. Benefiting from the focused current density in the grooves, the Li preferentially deposits in the grooves instead of on the surface, thus suppressing the Li dendrite formation during the Li plating/stripping process. With this in mind, both cycling life of the assembled Li–Li symmetric cells and Li–LiFePO4 (LFP) full cells is prolonged for over 5 times. The Li–Li symmetric cells assembled with the patterned Li exhibit excellent cycling stability for 800/400 ​h ​at 0.1/0.2 ​mA ​cm−2. More importantly, the 3–4 ​mg ​cm−2 LFP-loaded patterned Li/PEO/LFP cell achieves high capacity retention of 91.3% within 100 cycles at 0.5C, while different degrees of short-circuits occurred for the bare Li/PEO/LFP cells.

Introduction

High-safety and high-energy-density all-solid-state lithium batteries (ASSLBs) have attracted intense interest recently [[1], [2], [3], [4]]. Among various solid-state electrolytes (SSE), solid polymer electrolytes (SPEs) with high-flexibility, easy fabrication and low cost have been regarded as one of the most promising candidates closest to the practical application [[5], [6], [7], [8], [9]].

However, most SPEs present low mechanical strengths at operating temperatures, which significantly hinder their practical application in ASSLBs due to the Li dendrite growth [10,11]. To tackle the aforementioned issue, tremendous efforts have been focused on improving the mechanical properties of SPEs. The most widely adopted two strategies are the introduction of inorganic fillers with high modulus and fabrication crosslinking polymer networks. Such inorganic metal/non-metal oxides as Al2O3 [12], SiO2 [13], oxide-based SSEs like LLZO [[14], [15], [16]], LATP [17,18] were introduced into the SPEs to enhance the ionic conductivity as well as suppress Li dendrite growth. For instance, Garnet-type Li6.75La3Zr1.75Ta0.25O12 (LLZTO) with an ultra-high shear modulus of 55 Gpa was developed as an effective filler into the PEO matrix, which played important roles in enhancing the mechanical strength and inducing uniform Li+ distribution on the surface of Li anode as well, thus improved the Li dendrite suppression capability [19]. Nevertheless, the discontinuity of the particle fillers dispersed in the polymer matrixes shows the inability to suppress Li dendrite effectively. To tackle this issue, fabrication of 3D interconnected scaffolds via electrospinning [20], aerogel [21], hydrogel [22] and template methods [23] for polymer infusion has been developed as an alternative. Very recently, our group proposed to impregnate the PEO electrolyte into commercially available glass fibers, which significantly enhanced the mechanical strength of the SPE, even under a high temperature of 120 ​°C. The assembled Li–Li symmetric cells demonstrated excellent cycling stability for over 1000 ​h ​at a current density of 0.42 ​mA ​cm−2 (capacity:0.4 mAh cm−2) [24].

Alternatively, the fabrication of a polymer network via cross-linking strategy has also been verified to be effective in enhancing the mechanical strength of SPEs. For instance, a high mechanical strength of 12 ​GPa was realized by Guo’s group via photopolymerizing a branched acrylate onto the ion-conductive PEO matrix, which was strong enough to inhabit Li dendrite growth and achieved 130 ​h cycling life of assembled Li–Li symmetric cells at a high current density of 4 ​mA ​cm−2 [25]. Besides, electrolyte additives were developed to stabilize the Li anode surface to suppress the Li dendrite growth. In situ formation of Li3N on the surface of Li metal by introducing LiN3 into the SPE exhibited excellent cycling stability of over 650 ​h ​at 0.1 ​mA ​cm−2 (capacity:0.2 ​mA ​cm−2, which is over 6 times longer than that of LiN3-free counterpart [26]. In another study, a self-healing electrostatic shield (SHES) mechanism was proposed by Sun’s group by adding less than 1 ​wt% Cs+ into PEO electrolytes and prolonged the Li–Li symmetric cells’ life for almost one order of magnitude [27].

It should be noted that most strategies mentioned above are based on the SPE modification. Nevertheless, several challenges were still remained such as worsening energy density with the introduction of high-mass-density oxide fillers, time-consuming cross-linking process as well as the degradation of Li dendrite suppression capability because of electrolyte additives consuming during the plating/stripping process. In this regard, it is necessary to further explore more Li dendrite suppression methods based on both Li surface modification and SPEs decoration. Herein, a selective Li deposition strategy was proposed, for the first time, by constructing a patterned Li anode in SPE systems. The focused current density forced Li selectively deposited in the patterned grooves, which suppresses the Li dendrite formation. As a consequence, both the Li–Li symmetric cells and Li-LFP full cells assembled with patterned Li demonstrated over 5-times longer cycling life compared with the bare Li. The rational structure design of patterned Li will offer an opportunity for enhancing the metal dendrite suppression capability in other solid-state batteries such as Li/Na–S and Li/Na–O2 as well as Na-ion batteries.

Section snippets

Fabrication of patterned Li

The patterned Li was prepared by a template-press method. Firstly, a stainless steel mesh (SSM) was put on the surface of a Li foil and then added an external pressure of 30 ​kg ​cm−2 and kept for 10s. Then removing the SSM, a patterned Li with a grid structure was obtained.

Synthesis of PEO electrolyte

The PEO electrolyte was prepared by a solution casting method. Firstly, the mixed solution of PEO polymer (Mw: 1000000, 0.60 ​g), bis(trifluoromethylsulfonyl) imide (LiTFSI) salt (0.24 ​g) were dissolved in 20 ​mL

Results and discussion

As shown in Fig. 1a, for the bare Li, there are many defects existed on the Li anode surface Fig. S1), resulting in and non-uniform charge distribution and Li dendrite growth during the plating/stripping process [28]. The Li dendrite easily penetrates the SPEs, here the most wildly used PEO electrolyte was chosen as the representative, thus leading to the occurrence of a short-circuiting and shortened cycling life of the ASSLBs. On the contrary, when creating a grid structure on the surface of

Conclusion

In summary, we developed a selective Li deposition strategy to suppress Li dendrite formation in ASSLBs via rational designing a pattered Li. Due to the focused current density in the grooves, the Li preferentially deposits in the grooves rather than on the surface. Based on this concept, the Li–Li symmetric cells assembled with the pattered Li exhibit excellent cycling stability for 800 ​h (0.1 ​mA ​cm−2, 0.1 mAh cm−2) and 400 ​h (0.2 ​mA ​cm−2, 0.2mAh cm−2), respectively, which are over 5

CRediT authorship contribution statement

Xiaofei Yang: Conceptualization, Writing - original draft. Xuejie Gao: Conceptualization, Writing - original draft. Changtai Zhao: Methodology. Qian Sun: Writing - review & editing. Yang Zhao: Methodology. Keegan Adair: Writing - review & editing. Jing Luo: Writing - review & editing. Xiaoting Lin: Formal analysis. Jianneng Liang: Formal analysis. Huan Huang: Software. Li Zhang: Validation. Shigang Lu: Validation. Ruying Li: Resources. Xueliang Sun: Supervision.

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.

Acknowledgments

This work was partly supported by Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Research Chair Program (CRC), Canada Foundation for Innovation (CFI), Ontario Research Fund, China Automotive Battery Research Institute Co., Ltd, Glabat Solid-State Battery Inc. and University of Western Ontario. Qian Sun appreciates the support of ​MITACS ​Elevate ​postdoctoral ​program.

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