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Contents 1 Introduction Description of different battery types 3 2 Electrolyte 4 2.1. AEROSIL for lead acid gel batteries 4 2.2 Dynasylan for (Li-ion) batteries 5 3 Separators 6 3.1. Separators in lead acid batteries (SIPERNAT ) 6 3.2. Separators for Li-ion batteries (AEROSIL, AEROXIDE ) 7 4 Electrodes 9 4.1. Electrodes for Li-ion batteries (AEROXIDE ) 9 4.2. Titania as precursor material for lithium titanate 9 5 Global presence 10 6 Literature of Evonik 11 7 Product recommendation 11 2
1. Introduction The world of rechargeable batteries is changing. For the last decades, lead acid starter batteries have been the most prominent type of battery on the market. But since the greenhouse effect and global warming are regarded as global threats and since energy costs are increasing significantly, scientists and technicians are looking for new energy concepts worldwide. Battery technology plays an important role in solving the current problems and in making energy available in a better way. Renewable energy sources, like wind and solar energy, are becoming more and more important and the necessity for efficient intermediate energy storage is increasing. This can be solved, for example, by lead acid gel batteries (LAB) or lithium-ion batteries (Li-ion ). Nowadays, high-energy and high-power Li-ion batteries play an important role for new energy storage concepts in automobiles. Hybrid electric vehicles (HEV) as well as full electric vehicles (EV) are reliant on these battery technologies, which are currently developed intensively. Additionally, the new electric bike generation (e-bikes) requires an efficient rechargeable battery system based on advanced lead acid (gel, AGM / SiO 2 ) or Li-ion technologies. These few examples demonstrate the growing demand for new materials and technologies for efficient and environmentally friendly batteries. Evonik Industries, as one of the most important chemical suppliers to the battery industry, provides many sophisticated solutions for present and future battery systems. In gel batteries fumed silica is applied as thickening agent in the electrolyte. Precipitated silica is used as filler in separators for LAB while fumed products are used as filler and as well for coatings in Li-ion separator technology. Fumed titania is suitable as precursor material for the production of lithium titanate Li 4 Ti 5 O 12 an anode active material for Li-ion batteries. These are just a few examples from the extensive portfolio of Evonik for the battery industry. Ask us, challenge us we will find the right solution for your application. Our applied technology experts will provide optimum solutions for your advanced battery technology. Description of different battery types In general, batteries can be classified using the concept of physical and chemical batteries. The class of physical batteries consists of thermal cells and solar power batteries, while their chemical analogues include primary (non-rechargeable) and secondary (rechargeable) batteries. Various types of rechargeable batteries are known, including the four most common ones: Lead acid batteries Nickel cadmium batteries Nickel metal hydride batteries Lithium-ion batteries Solar battery Physical battery Thermal cell Battery Chemical battery Primary battery (not rechargeable) Rechargeable battery Lead acid battery Lithium-ion battery Lithium polymer battery Nickel cadmium battery Nickel metal hydride battery Other rechargeable batteries 3
General principle of a rechargeable battery 2. Electrolyte e - 2.1. AEROSIL for lead acid gel batteries NODEDischarge and ChargeAe - CATHODEBoth, lead acid and Li-ion batteries consist of the same major components the two electrodes (anode and cathode), a separator in between them and finally an electrolyte, which is responsible for the ion transfer during charge and discharge processes. Lead acid batteries are one of the oldest types of rechargeable batteries. Even though their energy-toweight ratio is low, the ability of the cells to supply a high surge current results in a high power-to-weight ratio. Due to their low costs, lead acid batteries are still gaining market shares, especially in these fields, where new battery systems are either too expensive or too demanding, particularly with regard to maintenance. Lead acid batteries are still the most cost effective battery type for the following applications: Starter batteries for automotive engines Traction batteries for golf caddies, fork-lifts, wheelchairs, cleaning machines Stationary batteries as power back-up for telecommunication and data centers, power plants, hospitals, renewable energy systems, emergency lighting, green energy plants Evonik products are present in the following battery components Lead acid battery Lithium ion battery Electrode material Separator Electrolyte SIPERNAT AEROXIDE AEROXIDE AEROSIL AEROXIDE AEROSIL Dynasylan History of lead acid gel batteries Conventional flooded cell lead acid batteries are problematic in view of safety, due to their liquid acidic electrolyte. Therefore, they should be used only in an upright position in order to prevent leaking or spilling of the highly corrosive sulphuric acid. In the late fifties, a new class of advanced lead acid battery based on gel technology was introduced. The gel battery is a type of valve-regulated leadacid battery (VRLA). In VRLA batteries no water needs to be added during their lifetime and the battery is sealed with valves. The acidic electrolyte is either fixed in the form of a gel or is absorbed in a glass fleece. 4
The advantages of gel batteries are: Almost maintenance-free Spillage-free Can be used in different positions / no need to be kept upright / operation irrespective of its position Possibility of high discharge currents Resistance to vibration, shock, extreme temperatures No acid stratification Deep discharge Fumed silica is used to gelify the sulfuric acid. The requirements for gel forming agents are challenging: High purity Chemical stable towards sulphuric acid, lead oxide, and lead Thickening and thixotropic behavior Medium to high surface area AEROSIL fumed silica fulfills these demands and provides our customers with the following benefits: Highly effective thickening Thixotropic behavior Electrochemically and chemically inert Stable viscosity High purity Prevention of acid stratification 2. 2. Dynasylan for Li-ion batteries Due to their special properties, organofunctional silanes act as highly efficient surface modifiers, as water and HF scavengers, and as solvents. Hence, they can act as additives for electrolytes in lithium ion batteries. In addition to increased reliability due to higher thermal stability and the lower risk of hydrogen and oxygen formation, increased durability and a higher number of load cycles can also be expected. 5
3. Separators 3.1. Separators in lead acid batteries (SIPERNAT ) The function of the separator is to prevent the physical contact of cathode and anode from eachother to avoid a short-circuit. Additionally, it must be permeable for ions, which move freely between the electrodes. To fulfill those contradicting properties, the separator has to be mechanical stable and porous at the same time. Due to the high porosity, protons can migrate from one electrode to the other and close the electrical circuit. Because of the non-conducting separator the electrodes are not in direct contact with each other. Separators for lead acid batteries can be made up of different polymers, such as polyethylene (PE), polyvinylchloride (PVC), resins or rubber. They vary regarding design (thickness, ribs), porosity, and composition of the ingredients. In comparison to the other polymers, the polyethylene based separators show a high flexibility and weld ability, making PE suitable for a preferred application in starter batteries. The main raw materials are PE (UHMW-PE), silica and oil. Selected additives are used, such as lubricants, wetting agents, carbon black. Benefits of the PE separator compared to other materials are: puncture resistance, flexibility, ability to be folded and sealed, oxidation resistance and low acid displacement. The function of silica is to make the separator porous. This is achieved by mixing the raw materials and by extruding the mixture to form a sheet. The oil is extracted from the sheet and the sheet becomes porous. The silica remains in the porous sheet and makes the surface of the PE separator hydrophilic and wettable for sulfuric acid allowing the protons to pass through the separator. The silica for battery separators needs to be tailormade to achieve the following properties: low electrical resistance of the separator material, good processing properties for the manufacturing process, specific morphology to control the separator shrinkage behavior during manufacturing and in service, and specific requirements for purity and trace elements. The Evonik grades SIPERNAT 325 C, SIPERNAT 325 AP, SIPERNAT BG 2, SIPERNAT 325 E and possibly new grades fulfill these market requirements excellently. Materials for separators in lead acid batteries PE PVC Rubber Rubber / PE Phenolic resin Strength Excellent Good Fair Excellent Good Flexibility Flexible Rigid Flexible Flexible Rigid Mean pore diameter (µm) 0.10 0.07 0.22 0.15 0.06 0.10 0.50 0.34 Pore Volume (%) 55 65 60 70 45 55 50 60 60 70 ER (Ωcm²) 0.120 0.130 0.250 0.110 0.140 Oxidation resistance Resists to Antimony transfer Excellent Excellent Good Good Excellent No No Yes Yes No 6
3. 2. Separators for Li-ion batteries (AEROSIL, AEROXIDE ) Similar to lead acid batteries, the basic function of the separator in Li-ion batteries is to prevent physical contact of anode and cathode from each other, while allowing lithium ions to move freely between the electrodes. Therefore, the separator is made of electrically insulating materials, exhibiting a high porosity. The basis of all micro porous membranes is a thermoplastic material, that prevents short circuiting by separating the electrodes and blocking ionic conductivity in case of thermal runaway. The separator itself does not participate in the chemical reaction. The performance of the battery, including energy and power density, cycle life and safety is directly affected by the separator. Various separator types are known for Li-ion batteries, including: 1 Micro porous membranes 2 Solid ion conductors 3 Gel polymer electrolytes The application of Li-ion batteries as energy storage systems in HEVs and full EVs requires an improvement of the currently used separators in order to increase the safety function significantly. Modification of these micro porous membranes with inorganic nanostructured particles, e.g. silica or alumina as fillers or coatings, results in an improved inorganic-organic hybrid membrane with a high porosity and enhanced thermal stability. Furthermore, the mechanical strength and electrolyte wetability is significantly increased. These inorganic fillers can either be integrated directly into the thermoplastic material or into a separate layer that is coated, laminated or coextruded on top of the membrane. Such a ceramic modified separator enhances enhances the mechanical stability and, therefore, leads additionally to an advanced protection against lithium dendrite growth inside the cell. 7
Requirements for Li-Ion battery separators Parameter Goal Thickness < 25µm Porosity > 40 % Pore size < 1µm Electrical resistance 2 ohms cm 2 Wettability Complete wetting by typical electrolytes Inorganic fillers like AEROSIL and ceramic layers with AEROXIDE greatly influence the characteristics and properties of the micro porous separator: Improve thermal stabiliy (high temperature melt integrity) Enhance mechanical strength improve electrolyte wettability Increase porosity Puncture strength > 300 g mil 1 Shrinkage High-temperature melt integrity < 5 % @ 90 C for 1 h > 150 C Shutdown temperature ~ 130 C Dimensional stability Should lay flat and not curl on the edges 8
4. Electrodes 4. 1. Electrodes for Li-ion batteries (AEROXIDE ) The two electrodes of a Li-ion battery act as host materials for the insertation of small Li + ions. Upon charge / discharge of the battery Li ions start to migrate out of one electrode active material, diffuse through the electrolyte filled separator, to finally insertate into the other electrode. As appropriate anode materials a huge variety of different carbonaceous compounds (natural & artificial graphite, hard and soft carbons) were used as hosts for the reversible storage of Li ions in between the carbon sheets. In general, the electrodes are formulated from the following materials: 1 Current collector 2 Electrode active material 3 Conductive material (e.g. carbon black) 4 Binder 5 Additives 4.2. Titania as precursor material for lithium titanate Carbon based anode materials exhibit a disadvantage: the formation of an (irregular) solid electrolyte interface (SEI) and the subsequent irreversible capacity decline upon first-time battery cycling. This phenomenon can lead to a decreased cycle life of the battery and represents additionally a safety risk, because of the potentially growth of lithium dendrites. Therefore, other types of anode active materials, especially for those batteries, which are designed for HEVs and full EVs, are currently developed intensively. Lithium titanate Li 4 Ti 5 O 12 seems to be an appropriate anode active material, mainly due its high safety. During the charge / discharge, i.e. lithiation and delithiation process, a significant volume change of the host material is not observed (zero-strain material), resulting in a stable anode structure. Furthermore, the formation of a SEI between the anode material and the electrolye does not occur, avoiding the irreversible capacity decline upon firsttime battery cycling. Li titanate can be synthesized from different Ti sources like Ti(OR) 4, TiCl 4 or TiO 2 and the use of a variety of Li salts (see table below). Two types of AEROXIDE materials AEROXIDE P 25 and AEROXIDE P 90 are recommended precursor compounds for the synthesis of Li 4 Ti 5 O 12. Different synthesis methods for the production of Li 4 Ti 5 O 12 Method Ti source Li source (examples) Sol-gel Ti(OR) 4, TiCl 4 Li 2 CO 3, Li(COOR), Li(OR) Electrochemical insertion TiO 2 LiClO 4, LiAsF 6, LiCF 3 SO 3 Solid-state reaction TiO 2 Li 2 CO 3, LiOH, Li 2 O Electrochemical TiO 2 LiCl (molten) Hydrothermal TiO 2 LiOH 9
5. Sites for production and applied technologies (AT) of SIPERNAT, AEROSIL and AEROXIDE Portland, USA AT-Center, Piscataway, USA Mobile, USA Waterford, USA Chester, PA, USA Antwerpen, Belgium Roussillon, France Wesseling, Germany AT-Center, Hanau-Wolfgang, Germany Leverkusen, Germany Rheinfelden, Germany Zubillaga-Lantaron, Spain Adapazari, Turkey Akoh, Japan AT-Center, Shanghai, Yokkaichi, Japan China (Production, AT-Center) Gajraula, Indien Nanping, China Ta Yuan, Taiwan Map Ta Phut, Thailand 10
6. Literature of Evonik Specialty Silica, Product Overview AEROSIL Product Overview Dynasylan Product Range Technical Overview: AEROSIL - Fumed silica 7. Product recommendation Lead acid batteries AEROSIL SIPERNAT Separator SIPERNAT 325 C SIPERNAT 325 AP SIPERNAT BG 2 SIPERNAT 22 S Electrolyte (gel) AEROSIL 200 AEROSIL 200 V AEROSIL 200 VS* *Regionally restricted availability Li-ion batteries AEROSIL / AEROXIDE Dynasylan Precursors for electrode active materials Separator Electrolyte AEROXIDE TiO 2 P 25 AEROXIDE TiO 2 P 90 AERODISP W 740 X AEROSIL AEROXIDE Alu C AEROXIDE Alu 65 AEROXIDE Alu 130 AEROXIDE C 805 AEROXIDE TiO 2 P 25 AERODISP W 740 X AERODISP W 630 Dynasylan VTMO Dynasylan (aminofunctional silanes as HF scavengers) 11
This information and any recommendations, technical or otherwise, are presented in good faith and believed to be correct as of the date prepared. Recipients of this information and recommendations must make their own determination as to its suitability for their purposes. In no event shall Evonik assume liability for damages or losses of any kind or nature that result from the use of or reliance upon this information and recommendations. EVONIK EXPRESSLY DISCLAIMS ANY REPRESENTATIONS AND WARRANTIES OF ANY KIND, WHETHER EXPRESS OR IMPLIED, AS TO THE ACCURACY, COMPLETENESS, NON- INFRINGEMENT, MERCHANTABILITY AND/ OR FITNESS FOR A PARTICULAR PURPOSE (EVEN IF EVONIK IS AWARE OF SUCH PURPOSE) WITH RESPECT TO ANY INFORMATION AND RECOMMENDATIONS PROVIDED. Reference to any trade names used by other companies is neither a recommendation nor an endorsement of the corresponding product, and does not imply that similar products could not be used. Evonik reserves the right to make any changes to the information and/or recommendations at any time, without prior or subsequent notice. AEROSIL, AEROXIDE, AERODISP, SIPERNAT and Dynasylan are registered trademark of Evonik Industries or its subsidiaries. Europe / Middle-East / Africa / Latin America Evonik Resource Efficiency GmbH Business Lines Silica & Silanes Rodenbacher Chausse 4 63457 Hanau-Wolfgang Germany PHONE +49 6181 59-12532 FAX +49 6181 59-712532 ask-si@evonik.com www.evonik.com North America Evonik Corporation Business Lines Silica & Silanes 299 Jefferson Road Parsippany, NJ 07054-0677 USA PHONE +1 800 233-8052 FAX +1 973 929-8502 ask-si-nafta@evonik.com Asia / Pacific Evonik (SEA) Pte. Ltd. Business Lines Silica & Silanes 3 International Business Park #07-18 Nordic European Centre Singapore 609927 PHONE +65 6809-6877 FAX +65 6809-6677 ask-si-asia@evonik.com 07-2015