臺灣博碩士論文加值系統

天然石墨的石墨化度高，具備良好的理論電容值，適合應用在鋰離子二次電池負極材料，但是其第一次不可逆電容量大，且經過短暫次數的循環伏安法測試後電容量將急速衰退，故在商業應用上受到限制。而在電池使用方面，天然石墨在鋰離子重覆嵌入、遷出下，層間結構易被破壞，所以電池壽命較短。故本實驗針對將片狀天然石墨，利用氣流粉碎機所製成之球狀天然石墨，改善其表面結構特性並進行研究。
為改善不可逆性電容量大的缺點，利用表面改質製程，在石墨表面披覆上一層呋喃樹脂，經1100℃熱處理後碳化形成非晶質碳材，透過這層非晶質碳膜，可以抑制鋰錯化合物嵌入石墨層間，來降低其不可逆電容量，並可降低其製造之成本。在結果與討論中，表面披覆了經由碳材鍵結所形成碳化之呋喃樹脂非晶質薄膜的球狀天然石墨，可有效強化原本不穩定的表面結構，提高電容量且降低不可逆性。在摻雜實驗中，借助矽的高理論電容量的特性，在天然石墨與呋喃樹脂的材料混合中，加入10-30wt.%矽粉體作為提升電容量的比較。實驗証明充電容量可有效提升，但礙於矽具有較大的體積膨脹問題與大的不可逆特性，添加量超過10%後仍難無法避免此項缺陷。
表面氟化處理方面，本實驗採用5at.% 氟濃度作為表面氟化的反應氣體。實驗在加熱反應過程中，表面的石墨碳材與氟元素間產生由C-F組成的離子鍵，而逐漸轉為SP2離子性的半共價鍵型態，此種結構具有導電性，而經過表面氟化處理過的石墨具有第一次不可逆電容量小、庫倫效率高的優點。

Natural graphite and carbonaceous materials are most promising materials as the anode for lithium ion batteries. Although natural graphite exhibits a high specific capacity, violent reversible capacity decay occurs after a few charge/discharge cycle tests. The drawbacks of performances are improved by surface modification. Surface modification of the anode composite material is investigated on spherical like-natural graphite and used as base material whereof it is prepared from flake into sphere shape by jet-milling process.
The carbon coating method is prepared from very component furan resin by heating process. Furan resin is changed into amorphous carbon material after heat treatment at 1100˚C. Furthermore, in the chapter of result and discussion, the carbon coating from furan resin heat treatment on the surface of spherical like-natural graphite which can strengthen graphite surface modification and promote the electrochemical characteristics by the effects of increasing C-C bonding. Carbon coating of furan resin on natural graphite can also inhibit the insertion of lithium complex into graphite and reduce irreversibility. The coulombic efficiencies are great improvement on natural graphite by carbon coating of furan resin. In otherwise, silicon powder has highly specific charging capacity as host material in anode. In our study, it is added into carbon coated graphite particles and from mixture to enhance the charging capacity wherein the composite is treated by carbon coating of furan resin. In the 10-30wt% addition of silicon particles, we determine that the electrochemical properties are superior to natural graphite at the first charging capacity; nevertheless, the violent decreasing discharge capacity is still hard to be avoided in high constituent composite material of silicon.
In the surface fluorination process, the formative fluorinated graphite production is treated under 5at% fluorine gas by heat treatment, and thereto is formed fluorine-graphite intercalation compounds of semi-covalent C-F bonding with sp2 planar of graphene layers. Furthermore, form the EDS analysis and the cycle test; we confirm that the forming C-F bonds can affect lithium ion energy during insertion/extraction. The improved electrochemical characteristics of surface fluorination in carbon coated with furan resin are observed with the first charge capacity.

Content

Acknowledge…………………………………………………………………………...i
English Abstract……………………………………………………………………….ii
Chinese Abstract……………………...………………………………….……………iv
Contents………………………………………………………………………………..v
Table Captions…………………………………………………………………....….viii
Figure Captions………………………………………………………………….…….x

Chapter 1 Introduction……………………………………………………..........1

Chapter 2 Background……………………………………………………...…...4
2.1 A summarized account of lithium ion battery…………………………………...4
2.2 Battery works and processes of production……………………………………5
2.3 Coin-type secondary lithium battery………………………………………….…7
2.4 Electrochemical descriptions of a secondary battery……………………………7
2.4.1 Energy density………………………………………………………………..….....8
2.4.2 Cycle life…………………………………………………………………………...8
2.4.3 Self-discharge rate………………………………………………………………….8
2.5 Comparison of application overview……………………..………...……………8
2.5.1 Lead/Acid…………………...………………………………………………..….....9
2.5.2 Nickel/Cadmium…………………………………………………………………...9
2.5.3 Nickel/Metal hydride……...………………………………………...……………10
2.5.4 Lithium-ion………..………………………………………………………..…….10
2.6 A summarized account of lithium ion material………………………………...11
2.7 Research of electrolyte…………………………………………………………14
2.8 Research of cathode materials………………………………………………….15
2.8.1 LiCoO2…………………...………....……………………………..….......16
2.8.2 LiNiO2………………………………...…………………..............……...16
2.8.3 LiMn2O4……...…………………………………………….............…….17
2.9 Research of anode materials……………………………………………………18
2.10 Carbon coating………………………………………………………………20
2.11 Surface fluorination……………………………………………..…………….20
2.12 Charge capacity improvement by adding silicon……...…………………..….21

Chapter 3 Experiment details…………………………………………...........38
3.1 Preparation of basic materials………………………………………………….38
3.2 Carbon coated graphite of furan resin by teat treatment……………………….38
3.3 Improvement of electrochemical characteristic by surface fluorination……….38
3.4 Enhancements of charge capacity by addition of silicon powder……………...39
3.4.1 Experiments of 325mesh-silicon powder…………………………………………40
3.4.2 Experimental comparisons with 325mesh/nano-scale silicon powder………..….41
3.5 Analysis of characteristics……………………………………………………...41
3.5.1 X-ray diffraction………………………...………………………..………………42
3.5.2 Raman spectroscopy………..…………………………………………………….42
3.5.3 Energy dispersive spectrometry…………………………………………….....….42
3.6 Electrochemical measurement………………………………………………….42
3.7 Developments of coin-type secondary lithium-ion cells……………………….43
Chapter 4 Results and Discussion……………………...………………..…..46
4.1 Electrochemical characteristics compare with natural graphite and carbon coated graphite……………………………………………………………………..…..46
4.1.1 DTA/TGA measurements……………...……...…………………..………………46
4.1.2 Scanning electron microscopy.……………………………...……...…………….46
4.1.3 Raman spectroscopy……………………………………………….……….....….47
4.1.4 X-ray diffraction………..…………..…………………………………………….48
4.1.5 Electrochemical characteristics………………………………….………….....….49
4.2 Enhancements of electrochemical characteristics by surface fluorination……..50
4.2.1 Scanning electron microscopy.……………………………...……...…………….51
4.2.2 Raman spectroscopy……………………………………………….……….....….51
4.2.3 X-ray diffraction………..…………..…………………………………………….52
4.2.4 Energy dispersive spectrometry analysis……………….…………….…….....….53
4.2.5 Electrochemical characteristics………………………………….………….....….54
4.3 Electrochemical characteristics compare to the additions of different size silicon powders………………………………………………………………………...56
4.3.1 Scanning electron microscopy.……………………………...……...…………….56
4.3.2 X-ray diffraction………..…………..…………………………………………….57
4.3.3 Raman spectroscopy……………………………………………….……….....….57
4.3.4 Electrochemical characteristics………………………………….………….....….58

Chapter 5 Conclusion….………….................................................................….96
Reference…………………………………………………...……………….……..98

Table Captions

Chapter 2
Table 2-1 The energy densities of the different battery technologies have being
used……………………………………………………...…………………………...23
Table 2-2 The processes of fabrication lithium ion batteries………………………..24
Table 2-3 All comparisons of the advantages, disadvantages, and typical
applications of secondary batteries…………………...……………………………...25
Table 2-4 The comparisons of electrochemical characteristics, wherein
between lithium metal and carbonaceous materials………………………..………...27
Table 2-5 Fundamental properties of most solvents are used for secondary
lithium-ion batteries at 25℃………………………………...……………..………...28
Table 2-6 Lithium salts for Nonaqueous Solutions……………………….………...29
Table 2-7 Comparison of cathode materials……………………………….………...30

Chapter 3
Table 3-1 A detail prescription of preparation materials………………………….…44

Chapter 4
Table 4-1 Structural properties and electrochemical characteristics of natural
graphite and carbon-coated graphite………………………….…………………...…62
Table 4-3 d002 spacing evolution of natural graphite (NG), fluorination
natural graphite (FNG), and furan resin 15wt.% carbon-coated graphite
(CNG15) and fluorination CNG (FCNG15) samples at 800℃ as a function
of reaction time…………………………..…………………….…………….…….…63
Table 4-4 Composition (at.%) of fluorination natural graphite (FNG) and
fluorination carbon-coated graphite (FCNG) samples……………………...………..64





















Figure Captions

Chapter 2
Fig. 2-1 The battery pumps electrons from its positive terminal to negative terminal, giving each electron a certain amount of energy. These electrons flow through the light bulb on their way back to the positive terminal. The Electrons
give up their energies in the bulb, which then produces light…………………….....31
Fig. 2-2 Secondary batteries compare with the volumetric energy and the
Gravimetric energy densities……………………………………….…………..……32
Fig. 2-3 Schematic diagrams of the solid-electrolyte-interface (SEI) film formed
at the surface of bare graphite and the composites of graphite selectively
deposited with metals: (a) Bare graphite processed under high humidity
, and (b) Composite processed under high humidity: : intercalated lithium
ion; : LiOH; : solvated Li+; ○: metal element (from Ref. [16])……….….33
Fig. 2-4 Structure of graphite intercalation compound LiC6 (a) Schematic illustration of stacking of graphite layers in AA••• way; (b) In-plane distribution
of Li in LiC6 (from Ref. [1])………………………………………………………....34
Fig. 2-5 Schematic diagrams of secondary lithium ion battery are during
discharge wherein the mainly consists are graphite/carbonaceous anode
and a lithium transition metal oxide such as LiCoO2, LiNiO2, and
LiMn2O4 as the cathode………………………………………………………………35
Fig. 2-6 Schematic diagram of electrical behaviors………………………………….36
Fig. 2-7 Structure of layered LiCoO2 (grey circles: Co3+ at the site of 3b,
solid circles: Li+ at the site of 3a, white circles: O2− at the site of 6c)
(from Ref. [1]).……………………………………………………….……..………..37

Chapter 3
Fig. 3-1 The structure of a coin-type secondary lithium-ion cell…………………….45

Chapter 4
Fig. 4-1 DTA/TGA profiles of the changes of furan resin with increasing
temperature……………………………………………………...…………………...65
Fig. 4-2 The SEM photographs of (a) spherical natural graphite and (b) 20wt.%
carbon-coated graphite by furan resin………………………………………………..66
Fig. 4-3 The SEM micrographs of 40wt.% carbon-coated graphite by furan resin; (a) some agglomeration is observed at 500× magnification; (b) shape and
surface morphology at 3500× magnification …………………………………...…...67
Fig. 4-4 Raman spectra of the natural graphite with different amounts of carbon-coated graphite formed by heat treatment at 1100C using furan
resin…………………………………………………………...……………………...68
Fig. 4-5 The R-value of two intensities (I1360/I1580) obtained by adding different
amount s of furan resin coating………………………………………………………69
Fig. 4-6 The X-ray diffraction patterns along the (002) plane of natural graphite and carbon-coated graphite with FN-10wt.% , FN-20wt.% , FN-30wt.% and the
FN-40wt.% samples………………………………………………………………….70
Fig. 4-7 The X-ray diffraction patterns at 2H(101) and 3R(101) plane of natural graphite and carbon-coated graphite with FN-10wt.% , FN-20wt.% ,
FN-30wt.% and the FN-40wt.% samples……………………….…………………...71
Fig. 4-8 The Discharge/charge profiles of (a) natural graphite and (b) the
FN-40wt.% samples………………………………………………………………….72
Fig. 4-9 The Cycling behavior of the discharge capacity profile of natural graphite, FN-10wt.% , FN-20wt.% , FN-30wt.% and the FN-40wt.%
samples……………………………………………………………………………….73
Fig. 4-10 SEM images of (a) natural graphite (NG); (b) fluorination NG (FNG)
and (c) fluorination carbon-coated graphite with furan resin15wt.% adding
amount (FCNG) treated at fluorination temperature 800C for 10 hours.……..….…74
Fig. 4-11 XRD patterns of natural graphite (NG), fluorination natural graphite
(FNG), carbon-coated graphite with 15wt.% furan resin (CNG15) and
fluorination carbon-coated graphite with 15wt.% furan resin (FCNG)
treated at fluorination temperature 800C for 10 hours…………………………...…76
Fig. 4-12 Raman spectra of natural graphite (NG), fluorination natural graphite
(FNG) and fluorination carbon-coated graphite with furan resin15wt.%
(FCNG) treated at fluorination temperature 800C for 10 hours………………...…..77
Fig. 4-13 R-value evolutions of natural graphite (NG), fluorination natural
graphite (FNG), carbon-coated graphite (CNG15) and fluorination
carbon-coated graphite (FCNG) treated at fluorination temperature 500 and
800C for 5 and 10 hours………………….…………………………….………….78
Fig. 4-14 Cycling behavior of the charge capacities of NG, FNG, and FCNG
samples treated at fluorination temperature 500 and 800C for 10 hours……….…..79
Fig. 4-15 SEM micrographs of (a) 325mesh-silicon, (b) nano-silicon, (c) spherical natural graphite, (d) composites of FN40, (e) GSF334 and (f)
GNF334………………………………………………………………………...…….80
Fig. 4-16 XRD patterns of (a) the natural graphite (NG) and carbon coating of 40 wt.% furan resin (FN40), (b) FN40, GSF514, GSF424, and GSF334, and (c)
GSF334 and GNF334 after 1100℃ heat treatment…………………….……………83
Fig. 4-17 Raman spectra show the NG, FN10, FN20, FN30, and FN40 after
1100℃ heat treatment…………………………………………………………...…...85
Fig. 4-18 Graph shows the R-values ratio of two intensities I1360/I1580 by
different concentration rates of furan coating………………………………….…….86
Fig. 4-19 Charge and discharge profiles in the first cycle and charge profiles in the fifth cycle test of the natural graphite and carbon-coated graphite of 40wt.%
furan resin (FN40) after 1100℃ heat treatment………………………………...……87
Fig. 4-20 Charge and discharge curves by heat treatment at 1100℃ of the (a) pure silicon, (b) NG, (c) FN40, (d) GSF514, (e) GSF334, (f) GNF514 and (g)
GNF334………………………………………………………………………………88
Fig. 4-21 Charge/discharge profiles of the GSF514 sample…………………….…...92
Fig. 4-22 Cycling behaviors of NG, FN40, and GSF samples……………...………93
Fig. 4-23 Cycling behaviors of NG, FN40, GSF334, and GNF334 samples……….94
Fig. 4-24 Coulombic efficiencies of GSF514, GSF424, GSF334, GNF514,
GNF424 and GNF334 samples………………………………………………….…...95

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