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Functional Electrolytes for Advanced Lithium Ion Batteries

Functional Electrolytes for Advanced Lithium Ion Batteries
Alternative Title
고성능 리튬 이온 전지 용 기능성 전해액 개발
Seong-Hyo Park
DGIST Authors
Park, Seong HyoLee. Ho ChunSong, Hyun Kon
Hochun Lee
Hyun-Kon Song
Issued Date
Awarded Date
2018. 8
Li-ion batteries, Polydopamine, FPS, I2, P2, additives, LiFSI, AN
Despite two decades of commercial history, enhanced lithium-ion batteries (LIBs) performance is required to satisfy the evolving electric vehicles (EVs) and energy storage system (ESS) market requirements which is essential for thermal stability, long-term cycle, safety, and fast charging. Here, we resolve these challenges using a mussel-inspired polydopamine (PD)-coating, novel additives, and analysis of superconcentrated electrolyte systems.

(1) it remains very difficult to simultaneously achieve both high rate capability and thermal stability in the graphite anodes of Li-ion batteries because the stable solid electrolyte interphase (SEI) layer, which is essential for thermal stability, impedes facile Li+ ion transport at the interface. The nanometer-thick PD coating layer allows the formation of a SEI layer on the coating surface without perturbing the intrinsic proper-ties of the SEI layer of the graphite anodes. PD-coated graphite exhibits far better performances in cycling test at 60 ℃ and storage test at 90 ℃ than bare graphite. The PD-coated graphite also displays superior rate capability during both lithiation and delithiation. The usefulness of the proposed PD coating can be expanded to various electrodes in rechargeable batteries that suffer from poor thermal stability and interfacial kinetics.

(2) Next study introduces 3-fluoro-1,3-propane sultone (FPS) as a novel SEI additive to replace VC and another popular SEI additive, 1,3-propane sultone (PS). Vinylene carbonate (VC) has been the best performing solid electrolyte interphase (SEI) additive for the current lithium-ion batteries (LIBs). However, it is also true that the current LIB technology is being stagnated by the limit set by VC. Electrochemical experiments confirm that the presence of an electron withdrawing fluorine group is favourable in terms of the anodic stability and the SEI forming ability. Considering the high anodic stability, the excellent cyclability, and the good thermal stability, FPS is an outstanding SEI additive that can expand the performance boundary of the current LIBs.

(3) The swelling issue by gas evolution at elevated temperatures (85-90 ℃) is one of the major challenges related to current Li-ion batteries (LIBs). We herein demonstrate that iodine (I2) as a redox shuttle additive, when its dose is properly determined, can suppress the swelling behavior of LiCoO2/graphite Al-pouch cells during storage at 90 ℃ without sacrificing other cell performances.

(4) Among the numerous additives, it remains very difficult to simultaneously adapt both spinel and layered cathode materials of Li-ion batteries. This study introduces a highly versatile new additive, sodium phosphate (P2), as a novel LIBs additive to improve the thermal stability in both spinel (LiMn2O4 and LiNi0.5Mn1.5O4) and layered (LiNi0.8Co0.1Mn0.1O2) cathode materials. Our investigation reveals that P2 additive scavenges harmful hydrofluoric acid (HF), effectively eliminates HF promoting metal dissolution from the cathodes, and forms a passivation layer on the cathode surface against electrolyte decomposition at high temperature. Considering the good thermal stability and the storage performance at high temperature, P2 additive is an outstanding additive that can be expand to regardless of the type of LIBs that suffer from poor thermal stability.

(5) Lastly, the superior rate capability of the superconcentrated LiFSI/AN electrolytes, claimed in recent reports, is scrutinized in relation to the active mass loading of the graphite electrodes. Compared to a conventional carbonate electrolyte, a superconcentrated (4.5 M) LiFSI/AN electrolyte exhibites enhanced rate capability in a low-loading (< 5 mg/cm2) graphite electrode. However, the superconcentrated electrolyte displays an inferior rate performance in a high-loading electrode (9 mg/cm2), which is commonly employed in commercial electrodes. The electrochemical impedance study reveals that the superconcetrated electrolyte enables the lower charge transfer resistance at the graphite/electrolyte interface (Rct), which is possibly associated with an unique solution structure in the concentrated electrolyte. However, as the graphite loading increases, the ion transport in the electrode pore (Rion) becomes dominant, which dilutes the merit of the low Rct in a superconcetrated electrolyte. This study indicates that the superior rate capability in superconcentrated solutions claimed in previous studies should be appreciated in conjunction with the electrode loading.
Table Of Contents
2.1 Electrochemistry 8--
2.1.1 Electromotive Force 8--
2.1.2 Electrode Potential 8--
2.1.3 Energy Storage 9--
2.2 Battery Theory 10--
2.4 Lithium-ion Batteries (LIBs) 11--
2.4.1 Anode Materials 12--
2.4.2 Electrolytes 13--
2.4.3 Solid Electrolyte Interphase (SEI) 14--
2.4.4 Additives 15--
2.4.5 Cathode Materials 15--
2.5 References 16--
Ⅲ. Mussel-Inspired Polydopamine-Coating for Enhanced Thermal Stability and Rate Performance of Graphite Anodes in Li-Ion Batteries 17--
3.1 Introduction 17--
3.2 Experimental 19--
3.2.1 Chemicals and electrode preparation 19--
3.2.2 Surface analysis 19--
3.2.3 Electrochemical measurements 19--
3.2.4 HF and H2O contents measurements 20--
3.2.5 Surface free energy measurements 20--
3.3 Results and discussion 21--
3.3.1 PD-treatment of graphite electrodes 21--
3.3.2 Effects of PD-coating on the formation and composition of the SEI layer 24--
3.3.3 Cycling and storage performance of PD-graphite at elevated temperatures 26--
3.3.4 Rate capability of PD-graphite 29--
3.3.5 Surface free energy analysis of PD-graphite 32--
3.4 Conclusions 34--
3.5 References 35
Ⅳ. Fluoropropane sultone as an SEI-forming additive that outperforms vinylene carbonate 40--
4.1 Introduction 40--
4.2 Experimental 41--
4.2.1 Chemicals 41--
4.2.2 Electrochemical measurements 41--
4.2.3 High temperature storage test 42--
4.2.4 Differential scanning calorimetry 42--
4.3 Results and discussion 43--
4.3.1 Anodic stability 43--
4.3.2 Formation and property of the SEI layer on the graphite anode 44--
4.3.3 Cyclability of LiCoO2/graphite cells at various temperatures 46--
4.3.4 Swelling behavior on elevated temperature storage 50--
4.4 Conclusions 51--
4.5 References 52--
Ⅴ. Iodine as a temperature-responsive redox shuttle additive for the swelling suppression of Li-ion batteries at elevated temperatures 55--
5.1 Introduction 55--
5.2 Experimental 57--
5.2.1 Chemicals 57--
5.2.2 Electrochemical measurements 57--
5.2.3 X-ray photoelectron spectroscopy 57--
5.2.4 Swelling tests 58--
5.3 Results and discussion 58--
5.3.1 Redox reaction of the I2 additive in LiCoO2/graphite cells 58--
5.3.2 Effects of I2 as an additive on swelling behaviors 63--
5.3.3 Proposed mechanism for swelling prevention by the I2 additive 67--
5.4 Conclusions 69--
5.5 References 71--
Ⅵ. A versatile sodium phosphate additive for enhanced thermal stability of spinel and layered cathodes of Li-ion batteries 73--
6.1 Introduction 73--
6.2 Experimental 74--
6.2.1 Chemicals and electrode preparation 74--
6.2.2 Electrochemical measurements 75--
6.2.3 Material Characterization 75--
6.3 Results and discussion 76--
6.3.1 Formation and property of the CEI layer on the cathodes 76--
6.3.2 The effect of P2 additive 78--
6.3.3 Cycling and storage performances 81--
6.4 Conclusions 88-
6.5 References 89--
Ⅶ. Analysis of physicochemical properties and superior rate performance of superconcentrated salt electrolytes 92--
7.1. Introduction 92--
7.2 Experimental 95--
7.2.1 Chemical and electrode preparation 95--
7.2.2 Electrochemical measurements 95--
7.3 Results and discussion 96--
7.3.1 Ionic conductivity and reductive stability against Li metal 96--
7.3.2 The 1st cycle behaviors in superconcentrated AN electrolytes 97--
7.3.3 Rate capability 99--
7.3.4 EIS analysis 101--
7.3.5 Al and SUS corrosions 102--
7.4 Conclusions 104--
7.5 References 105--
Summary (in Korean) 106
Energy Science and Engineering
Related Researcher
  • 이호춘 Lee, Hochun 에너지공학과
  • Research Interests Lithium-ion batteries; Novel Materials for rechargeable batteries; Novel energy conversion;storage systems; Electrochemistry; 리튬이차전지; 이차전지용 신규 전극 및 전해액; 신규 에너지변환 및 저장 시스템; 전기화학
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Department of Energy Science and Engineering Theses Ph.D.


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