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C. Wurm et al.
(Fig. 5.9b). Graphite offers only a few “points of entrance” for lithium (at the front
edges of the long-ranging layer areas) to enter the lattice, from where it has to
diffuse into the center of the long-ranging crystalline domains. Amorphous carbons,
on the other hand, offer more points of entrance. The distribution of lithium within
the ordered strata is also very quick, since the diffusion distances are very short.
Moreover, these domains with short-range order are also connected to each other,
lowering the tendency to delaminate. Therefore, amorphous carbons exhibit a
better cycling stability from an electrochemical point of view, especially at higher
charging rates (C rates).
5.4Production and electrochemical characteristics of C/Si
or C/Sn components
As with graphite, lithium is inserted into silicon in different, well-defined twophase plateaus with well-defined chemical compounds at the beginning and end
of the plateaus (Fig. 5.10). The composition and the respective potential levels vs.
lithium are as follows : Si/Li12Si7 (332 mV); Li12Si7/Li7Si3 (288 mV); Li7Si3/
Li13Si4 (158 mV); Li13Si4/Li21Si5 (44 mV). The theoretical specific capacity for the
maximum amount of lithium intercalated into silicon is 4,212 mAh/g . This
currently is the highest known possible capacity of an alloy. The insertion of lithium
in tin (Sn) follows several steps, similar to silicon. At room temperature, these are
for the most part easily detectable in the first cycle, as shown in Fig. 5.10b. The
theoretical specific capacity for Li4.4Sn is 993 mAh/g.
A large amount of lithium forms alloys with silicon and tin, thus resulting in
a big change in volume during intercalation/deintercalation. This in turn causes
the loss of the well-defined insertion steps during cycling and leads to amorphization of the material . This destruction of the crystalline structure is similar
to inner “grinding”, which decreases the cycling stability considerably. Extremely
Fig. 5.10 (a) Lithium insertion in silicon and tin (Sn), (b) lithium insertion in Sn, measured at
two different temperatures 
5 Anode materials for lithium-ion batteries53
Fig. 5.11 (a) Influence of silicon particle size on cycling in comparison with the theoretical
capacity for graphite , (b) influence of the binding agent on the cycling stability of anodes
based on C/Si 
small particles (down to the nano range) are used to reduce this effect (Fig. 5.11a).
A further improvement of the cycling stability is achieved by employing mainly
carbon composites; i.e., nanoparticles are integrated into carbon or graphite matrices, for example. However, this reduces the specific capacity.
Reactive binding agents are used in another approach to improve cycling stability. They cause an additional stabilization of the composite anode (Fig. 5.11b).
Lithium titanate as anode material
The lithium titanate (LTO), which crystallizes as spinel (Li4Ti5O12), reversibly intercalates lithium at 1.55 V (Fig. 5.12a) and reaches a reversible capacity of around
160 mAh/g (Li7Ti5O12). Intercalation/deintercalation of lithium causes almost no
change in particle volume in this process. The whole process consists of two phases
with a distinct flat plateau within the stability window of the electrolyte. No SEI is
Fig. 5.12 (a) Galvanostatic curve of lithium titanate (LTO) with lithium metal as counter electrode and (b) cycling of lithium titanate at 60 °C 
C. Wurm et al.
formed, and cell impedance is very low. All these parameters are the reason for the
cell’s very good cycling stability (Fig. 5.12b) and safety characteristics.
The disadvantage of this material is its very low electrical conductivity and resulting relatively poor performance. Hence, the particles should be as small as possible,
preferably in the nano range, and additionally coated with conductive carbon. These
measures improve the power and service life of lithium titanate. Its energy density
remains low, nevertheless, owing to the low specific capacity and the high potential
level vs. Li/Li+ (Fig. 5.1). Lithium titanate is therefore especially suitable for large
cells in stationary applications or for cells in areas with very high power requirements (e.g., hybrid vehicles).
Anode active materials – outlook
Table 5.1 shows a qualitative comparison of the most important anode active
materials in regard to the essential characteristics such as energy, power, service
life, and safety. This assessment reflects the authors’ state of knowledge at the
time of writing and merely provides a basis for approximate orientation and
Taking into consideration the above-mentioned property profiles, the following
materials are currently the most significant anode active materials (depending on
the application): synthetic graphite, natural graphite, amorphous carbon (hard and
soft carbons), and lithium titanate. Graphite has the most balanced profile and, as a
result, by far the largest market share. However, composites (in this context mainly
C/Si) will most likely gain in importance in the long-term future, depending on
the development. Examples of these are silicon alloys, non-silicon alloys such as
Table 5.1 Qualitative assessment of the property profiles of the most important anode active
materials. This assessment is merely a snapshot that needs to be updated as active materials and
the lithium-ion battery system evolve, since intensive research is currently being carried out
Lithium titanate (LTO)
C/Si or C/Sn composite
5 Anode materials for lithium-ion batteries55
LiNiMMO2 LiNiPO4, 5 V
High voltage LiCoPO , 5 V
LiMnPO4, 4 V
5 V spinel
ceramic coating Non-wovens
Fig. 5.13 Raw material road map for lithium-ion batteries  (Source Avicenne Compilation,
Kai-Christian Moeller, Fraunhofer ISC)
tin-based alloys, and metallic lithium. An overview is presented in Fig. 5.13, the
current raw material road map for lithium-ion batteries .
Copper as conductor at the negative electrode
In a lithium-ion cell there typically are two different metal foils that have the
function of collecting the current. The negative electrode consists of copper and
graphite; the positive electrode is made of aluminum which is coated with cathode
material. The electrochemical characteristics of copper are an important reason for
5.7.1 Requirements for the copper foil
The most important requirement for the copper collector is to collect electrons while
remaining electrochemically stable. These requirements are fulfilled very well by
pure copper. It has the second-highest electrical conductivity of all metallic mater
ials (after silver) with 58 MS/m. Its positive electrochemical potential results in
good corrosion resistance.
Furthermore, its surface must allow good adhesion of the chemically active anode
material (slurry). Its mechanical strength must be high enough for the foil to survive
C. Wurm et al.
the production of the cell. It is essential that the weight and price of large-format
lithium-ion batteries are kept low for them to be used as an affordable mass product
in electric vehicles. This is ensured by employing the most cost-efficient manufacturing process for foils that are as thin as possible.
The thickness of the copper foil mainly used at the moment is 10 μm. This thickness is determined based on the process requirements and the necessity to transport the electrons with a minimum loss of potential. Generally, it is not desirable to
employ thicker copper foils because copper accounts for around 10 % of the battery
mass. However, there are high-power cells with copper foils with a thickness of up to
18 μm and, on the other hand, high-energy cells with foils with a thickness of 8 μm.
Copper forms a slight oxide layer during storage. Therefore, the surface looks
darker and less shiny. Rough copper has more contact points with oxygen because
of its larger surface and therefore oxidizes more strongly. A copper foil with low
oxidation is preferred for a good coating.
Typically, the copper used in standard high-power cells is smooth copper, in spite
of the fact that a rougher copper surface provides for a larger contact surface for
the graphite and the binding agent, allowing faster charging and discharging of the
battery. The reason for this might be the size of the carbon particles, because adhesion is not influenced substantially with a typical particle size of 20 μm and foil
roughness of 1 to 2 μm.
Impurities in the copper decrease the service life of lithium-ion batteries. Residues from production such as oils and fats (RA copper) are not acceptable.
Coating the foil with graphite is a critical process step. In this context it is important to be able to use long coils free of joints. Each stop and restart increases the
reject rate. Furthermore, the copper should be mechanically stable and have no variations in weight per unit area.
5.7.2Comparison of RA copper foil with electrolytically
produced copper foil
Basically, there are two production processes for manufacturing copper foils: rolling
For the former, an industrial copper cast block is alternately rolled and heated
until the required foil thickness is reached. The result is a well-rolled material with
a fine granular structure that is elongated in the direction of rolling. Both surfaces
are shiny and have the same typical rolling structure.
Electrodeposited copper is manufactured as follows: Copper ions are electrolytically deposited from a copper sulphate solution onto steel or titanium drums
and rolled up into copper foil. This process is in accordance with Faraday’s law. It
stipulates that time and amperage determine the thickness of the deposited copper.
The copper grows dendritically. It is possible to modify this typical structure by
means of inhibitors in the solution. The resulting foil has differing surfaces. The
surface facing the drum is smooth and shiny; the surface facing away from the drum
is rougher. The grains are visible through the microscope.
5 Anode materials for lithium-ion batteries57
Both RA copper and electrodeposited copper may be used to produce cells for
l ithium-ion batteries. Availability and costs, especially of the very thin foils (10 μm)
that are currently demanded most, are the main reasons for the preference of electrodeposited copper.
5.7.3 Substitution of aluminum for copper?
Lithium ions are intercalated into the negative electrode (anode) while a lithium-ion cell is charging. The electrode material, typically graphite, expands by 10 %
during this process. The graphite regains its original volume when the lithium ions
The lithium ions would not only be intercalated into the graphite if aluminum
was used but also inserted into the conductor, thus forming an aluminum-lithium
alloy. The reverse process would occur during discharging. The aluminum would be
degraded after only a few cycles and would be useless as a current collector.
However, if the negative electrode consisted of lithium titanate instead of graphite,
a different picture would emerge. The electrode potential of Li4Ti5O12 is about 1.4 V
higher than that of graphite (cell voltage is around 1.4 V lower). This would prevent
the lithium ions from being intercalated into the aluminum. Therefore, aluminum
is preferred over copper for cost-related and weight-related reasons. Li4Ti5O12 is
employed mainly in stationary applications because of its lower cell voltage.
1. Abraham KM (1993) Electrochimical Acta 38:1233
2. Matsuda Y (1989) Nihon Kagaku Kaishi 110:1
3. Peled E (1979) J Electrochem Soc India 126:2047
4. Bolloré (www.bluecar.fr/de/pages-innovation/batterie-lmp.aspx)
5. Armand M (1980) In: Broadhead J, Steele BCH (ed.) Materials for advanced batteries.
Plenum Press, New York, pp. 145 – 150
6. Nishi Y (1998) In: Wakihara M, Yamamoto O (eds.) Lithium ion batteries. Wiley-VCH, New
York, p. 181
7. Megahead S, Scrosati B (1994) J Power Sources 51:79
8. Dahn JR et al. (1994) In: Pistoia G (ed.) Lithium batteries–new materials, developments, and
perspectives, industrial chemistry library. Elsevier, Amsterdam, pp. 1 – 47
9. Broussely M, Biensan P, Simon B (1999) Electrochim Acta 45:3
10. von Sacken U, Nodwell E, Sundher A, Dahn JR (1994) Solid State Ionics 69:284
11. Jossen A, Wohlfahrt-Mehrens M (2007) Overview on current status of lithium-ion batteries.
In: 2nd International renewable energy storage conference, Bonn, 19 – 21 Nov 2007
12. Castner JH (1893) GB 19089
13. Acheson EG (1895) US 568 323, 1895
14. Marsh H, Griffiths JA (1982) A high, resolution electron microscopy study of graphitization
of graphitizable carbon. International Symposium on Carbon, Toyohashi, p. 81
15. Omaru A, Azuma H, Nishi Y (1992) Sony Corp., Japan Patent Application: WO 92-JP238
16. Sekai K, Azuma H, Omaru A, Fujita S, Imoto H, Endo T, Yamaura K, Nishi Y, Mashiko S,
Yokogawa M (1993) J Power Sources 43:241
C. Wurm et al.
17. Winter M, Besenhard JO, Spahr ME, Novák P (1998) Adv Mater 10:725
18. Harris SJ (LithiumBatteryResearch.com) (2009) on YouTube; S.J. Harris, A. Timmons, D.R.
Baker, C. Monroe. Chem Phys Letters 2010 485:265
19. Peled E (1979) J Electrochem Soc., 126, p. 2047
20. Orsini F, Dupont L, Beaudoin B, Grugeon S, Tarascon J-M (2000) Int J Inorg Mater 2:701
21. Peled E, Golodnitsky D, Ardel G (1997) J Electrochem Soc 144:208
22. Dahn JR, Zheng T, Liu Y, Xue JS (1995) Science 270:590
23. Liu Y, Xue Js, Zheng T, Dahn JR (1996) Carbon, 34:193
24. Dahn JR (1997) Carbon 1997, 35:825
25. Wen CJ, Huggins RA (1981) J Solid State Chem 37:271
26. Weydanz WJ, Wohlfahrt-Mehrens M, Huggins RA (1999) J Power Sources 81 − 82:237
27. Limthongkul Pimpa, Jang Young-Il, Dudney Nancy J, Chiang Yet-Ming (2003) J Power
Sources 119–121:604 – 609
28. Huggins RA (1999) J Power Sources 81 – 82:13 – 19
29. Graetz J, Ahn CC, Yazami R, Fultz B (2003) Electrochem Solid-State Lett 6(9):A194 – A197
30. Hochgatterer NS et al (2008) Electrochemical and solid-state letters 11(5):A76 − A80
31. Zaghib K, Simoneau M, Armand M, Gauthier M (1999) J Power Sources 81 – 82:90
32. Pillot C (2011) The rechargeable battery market past and future. Batteries 2011, 28 – 30 Sept
Electrolytes and conducting salts
Christoph Hartnig and Michael Schmidt
6.2 Electrolyte components���������������������������������������������������������������������������������������������������� 60
6.2.2 Conducting salts�������������������������������������������������������������������������������������������������� 62
6.3 Functional electrolytes ���������������������������������������������������������������������������������������������������� 67
6.3.1 Calendar life and cycling stability ���������������������������������������������������������������������� 67
6.3.2 Safety and overcharging protection �������������������������������������������������������������������� 70
6.4 Gel and polymer electrolytes�������������������������������������������������������������������������������������������� 71
6.5 Electrolyte formulations – customized and distinct �������������������������������������������������������� 73
“Chemistry gets it done.” High-duty lithium-ion batteries of today and especially
those of the future are not conceivable without advances in the development of
materials. Chemistry will have to play a significant role in that. By employing innovative concepts for the materials, it will have to optimize the battery technology
in terms of energy density power density as well as cycle and calendar life and thus
open the door to electric mobility and stationary storage of renewable energy.
The development of new electrolyte systems for lithium-ion batteries is of para
mount importance, alongside the development of new electrode materials and
C. Hartnig (*)
Heraeus Deutschland GmbH & Co. KG, Heraeusstraße 12-14, 63450 Hanau, Germany
BASF SE, GCN/EE – M311, 67056 Ludwigshafen, Germany
© Springer-Verlag GmbH Germany, part of Springer Nature 2018
R. Korthauer (ed.), Lithium-Ion Batteries: Basics and Applications,