|Title:||Development of carbon cloth-based flexible lithium batteries|
|Advisors:||Zheng, Zijian (ITC)|
Lithium cells -- Materials
Hong Kong Polytechnic University -- Dissertations
|Department:||Institute of Textiles and Clothing|
|Pages:||xvi, 133 pages : color illustrations|
|Abstract:||The endless demand for advanced flexible and wearable electronics has driven the increasing interest in the development of deformable electrochemical energy storage devices (EESDs), especially flexible lithium-ion batteries (LIBs). Hitherto, there are commercially available prototypes of flexible smartphones like the Samsung Galaxy Fold, which, however, still shows limited flexibility restricted by the bulky and rigid LIBs and other components. Despite the great achievements in recent years, seldom commercial products of LIBs can be found to meet the needs of both high flexibility and high energy density. The configuration of the traditional LIBs is composed of stacked metal-foil-supported electrodes (MFEs), which are not suitable for the implementation of high flexibility. Besides, the energy density of the conventional LIBs based on graphite anode has reached its bottleneck, propelling the exploration of novel materials. Moreover, important factors like safety issues should be considered when the flexible LIBs are applied to wearable electronics. Thus, the flammable and toxic liquid electrolytes are expected to be substituted by the nonvolatile and thermal-tolerant solid-state electrolytes (SSEs) to eliminate the potential safety hazards. Taking one thing with another, the successful development of flexible and high-energy LIBs relies on the innovation of materials, design of electrodes, and renewal of cell configurations. Herein, we try to address the aforementioned challenges by developing carbon cloth (CC) based electrodes and LIBs. Three different types of LIBs are fabricated, and the electrochemical and mechanical performances are characterized. It shows that the flexibility of the CC-based electrodes can be well maintained while presenting a high energy density after assembled into full cells. Firstly, a polymer-assisted metal deposition (PAMD) method is applied to enable the uniform Cu coating on the carbon fiber for the enhancement of electrical conductivity. The mechanical and electrochemical properties of the pristine CC and Cu-coated CC (CuCC) as flexible hosts for lithium-ion intercalation are tested and compared. The results reveal that the Cu coating increases the electrical conductivity of the CC by more than one order of magnitude with a slight decrease of the original electrochemical properties. Stable cycling for more than 300 cycles of the full cells is demonstrated when the CC and CuCC electrodes are assembled into large pouch cells with high loading LiNi0.6Co0.2Mn0.2O2 (NCM622) cathodes. The good electrochemical performances of the CC and CuCC-based electrodes originate from the robust stability of the lithium-ion intercalation chemistry.|
Furthermore, to increase the energy density and cycling lifetime of the CC and CuCC based LIBs, a direct-contact prelithiation method is adopted. The lithium ions quickly intercalate into the CC and CuCC electrodes spontaneously during the prelithiation process, which provides an extra amount of active lithium for the electrodes and leads to a unique hybrid lithium metal/ion storage behavior. Consequently, the initial Coulombic efficiency (ICE), cycling lifetime, and energy density of the assembled cells based on the prelithiated electrodes are significantly increased compared to that of the untreated one. The capacity retention can be as high as 84% after 1000 charge/discharge cycles and the as-prepared pouch cell shows very good electrochemical stability even after bending 400 times. The hybrid lithium metal/ion storage mechanism shows great promise for the preparation of high energy density and stable LIBs. Last but not the least, an in-situ polymerization method is applied for the construction of quasi-solid-state lithium metal batteries (QSSLMBs) based on the CuCC-based composite lithium anode. The ionic conductivity and electrochemical properties of the gel electrolyte are investigated and optimized for the stabilization of the composite lithium metal anode. Benefit from the unique open porous structure of the composite anode, the UV light can penetrate through the electrode and induce the in-situ gelation of the precursor. The electrochemical performances of the full cell are significantly promoted because of the low interfacial resistance compared to that of the ex-situ fabrication. As a proof-of-concept, the assembled bipolar stacked QSSLMBs run stably for more than 50 cycles at room temperature with a very high discharge voltage of 6.6 V and neglected capacity loss. The safety and flexibility of the as-prepared cells can be notably enhanced due to the higher thermal stability and mechanical property of the gel electrolyte. In conclusion, the excellent mechanical and electrochemical properties of the CC-based electrodes as anodes for flexible and stable LIBs are demonstrated. Three different types of LIBs are assembled and investigated including the pure lithium-ion battery, hybrid lithium metal/ion battery, and lithium metal battery. Three different strategies are adopted to enhance the performances of the CC-based LIBs. The PAMD method is used for the increase of electrical conductivity of pristine CC. The direct-contact prelithiation method is used for the enhancement of energy density and cycling stability of the full cell. And the in-situ solidification is used for the construction of safer batteries. Accordingly, flexible and stable LIBs with high energy density and safety can be obtained. However, further exploration is inevitable for the optimization of full cells, especially for the cathode side.
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