Quality Requirements of Lithium Ion Battery Separators

Business Challenge
Lithium-ion batteries have one of the best energy-to-weight ratios, no memory effect, and a slow loss of charge when not in use. This makes them one of the most popular types of batteries for portable consumer electronics in today’s marketplace. Lithium-ion batteries can be found in cameras, laptops, power tools, toys and more. However, as recent well-publicized recalls demonstrate, they can pose a risk of fire and overheating. In addition, they can suffer from a reduced lifespan if not properly treated. As a result, new and stricter requirements are being implemented globally to address potential hazards, leaving manufacturers and purchasers of products containing lithium-ion batteries to meet increasing requirements and overcome safety concerns.

Lithium Ion Battery Separators

A Lithium Ion battery Separator is a permeable membrane placed between the anode and cathode of a battery. The main function of a separator is to keep the positive and negative electrodes, the cathode and anode respectively, apart to prevent electrical short circuits while also allowing the transport of ionic charge carriers which are needed to complete the circuit during the passage of current in an electrochemical cell.
As mentioned above, separators are power-driven spacers and can be produced with fiberglass cloth or flexible plastic films made from nylon, polyethylene or polypropylene. It must be absorbent and slim to allow the charged lithium ions to pass without obstruction and it should take up the minimum of space allowed, leaving available space for the cathode active elements. The separators must be able to withstand penetration and branching moss-like crystalline minerals in order to prevent the electrodes from contamination. If the separator breaks down or is infiltrated, this will weaken high power cells end results.

Properties of Polymer Separators

• Chemical Stability
• Thickness of Separator
• Porosity of Separator
• Pore Size
• Permeability
• Mechanical Strength
• Wet ability
• Stability
• Thermal Capabilities 

Thickness of Separator
A battery separator must be relatively thin in order to facilitate the high energy and power densities of the battery. However, if the separator is too thin, it can decrease the mechanical strength and safety of the battery. Additionally, a separator should have uniform thickness in order to support the long like cycle of a battery. In current technologies, 25.4μm is generally accepted as the standard width. The thickness of a polymer separator can be measured using the T411 om-83 method developed under the auspices of the Technical Association of the Pulp and Paper Industry

Permeability
The separator should not limit the electrical performance of the battery. Usually the presence of a polymer separator will increase the resistance of the electrolyte by a factor of four to five. The ratio of the resistance of the separator filled with electrolyte divided by the resistance of the electrolyte alone is called the MacMullin number. Air permeability can be used indirectly to estimate the MacMullin number. Air permeability is expressed in terms of the Gurley value, which is defined as the time required for a specific amount of air to pass through a specific area of the separator under a specific pressure. The Gurley value reflects the tortuosity of the pores, when the porosity and thickness of the separators are fixed. A separator with uniform porousness is vital to the long life cycle of a battery. Deviations from uniform permeability will result in uneven current density distribution, which causes the formation of Li crystals on the graphite anode.

Mechanical Strength
The separator must be strong enough to withstand the tension of the winding operation during battery assembly. The mechanical strength of the polymer separator is also very important. Mechanical strength is typically defined in terms of the tensile strength in two directions, the machine direction and the transverse direction, and terms of the tear resistance and puncture strength. All of these parameters are defined in terms of Young’s modulus.

Solutions 
To meet the requirements of battery separators and ensure the safety of manufacturers and end-user, we must control the quality of separators used in Lithium Ion battery. Therefore, the related test should be conducted for battery separators, such thickness measurement, permeability analysis and mechanical tensile strength testing. Each testing needs a high precise testing machine in order to get an accurate test results. Labthink instruments Co., Ltd is the only manufacturer of testing equipment professionally for thin film filed. Everything equipment they have is strictly applying to international standards and considered the manufacturers and users benefits of batteries

More detail infomation please contact us via labthinkchina@gmail.com.

Further Improvements on Performance of Weighing Method Water Vapor Transmission Rate Tester

Abstract: weighing method is the basic testing method for water vapor transmission rate measurement. After realizing automatic testing of water method, Labthink has made a series of innovative improvements on weighing method water vapor transmission rate tester with higher testing efficiency and better capability for extension. Thus, customized demands for desiccant method testing and inverted water method testing, as well as testing demands for special samples can be met.
Keywords: water vapor transmission rate , WVTR , weighing method , testing efficiency , inverted water method
Weighing method has long been the basic testing method for water vapor transmission rate testing with the widest applications, which can be subcategorized into desiccant method and water method, etc. The method needs manual operation in its early stage to accomplish the testing; yet, the relevant instruments are low in automation. Since high efficiency and multi-function are the trend for instrumental development, Labthink has, after introducing the first water method water vapor transmission rate tester of the world in 2003, made a series of innovative improvements on weighing method water vapor transmission rate instruments, and introduced Labthink PERME W3/031 Water Vapor Transmission Rate System with strengthened extension capability. Customized demands for desiccant method testing and inverted water method testing, as well as testing demands for special samples can be met. 




1.Higher Testing EfficiencyCommonly, it’s mistakenly held that weighing method is low in testing efficiency. No matter which method is applied, there is not much difference in time to realize permeation equilibrium between the sides of the sample. This is because the permeation performance of the sample is definite, and the only influential factor would be the fluctuation of ambient environment. Therefore, what truly influence the testing duration is the testing interval selected by the operator and the permeation equilibrium determined by the operator; of which, the latter is more influential. 
Generally, instruments of weighing method are in strict accordance with the testing standards in determining permeation equilibrium. In other words, permeation equilibrium would be considered to have been realized when the changing rate is lower than a certain rate. It’s usually applied by the sensor method instruments with a fixed testing duration, after which the instrument would be assumed to have achieved equilibrium. In practice, slight changes during permeation process would greatly influence the judgment on proportion mode, and no influence on fixed duration testing mode. However, it’s doubtful for the latter to achieve permeation equilibrium when the test ends. 
The barrier properties of all the samples to be tested would also influence the testing efficiency. Though each sample is tested individually in the multi-chamber weighing method instrument, the testing result could only be issued when the tests on all the samples have finished. Thus, testing efficiency depends on the sample with the best barrier property among the samples. Such low testing efficiency would be further influenced by the diversity of samples in the multi-chamber instruments, a problem more serious when testing results are in urgent need. 
As it’s required by the standards, the reliable testing results can only be issued after 3 testing data for each sample are obtained. Thus, Labthink specially develops a three-chamber testing instrument: Labthink PERME W3/031 Water Vapor Transmission System. The instrument has perfectly realized independent three-chamber testing with its patent weighing mechanism. Individual testing data for three samples can be obtained in one test. Meanwhile, since samples of the same material would not fluctuate much, the issuing time of testing data would be quite near. Therefore, higher testing efficiency can be realized when the three chambers are testing samples of the same material. 

2.Better Testing Accuracy Weighing method is the arbitral method for water vapor transmission rate testing, whose data accuracy is of vital importance. The structural optimization and most excellent components have guaranteed Labthink PERME W3/031 Water Vapor Transmission Rate System to realize highest testing accuracy in the world. Meanwhile, its humidity and temperature control capability are far superior to requirements of standards. It has better wind speed regulating function and faster calibration means. All those guarantees the wide applications of W3/031 for the water vapor transmission rate measurement of plastic films, composite films, sheets, high barrier materials, back sheets, foils, waterproof materials, thermal insulation materials and other materials applied in construction, medical and other fields. Thus, the testing subjects have expanded from packaging materials to textile, rub and building materials as well as new materials such as corrugated paper and back sheets applied in solar cell. 

3.Supporting Inverted Cup MethodInverted cup method, a subtype of weighing method, is to clamp the film or sheet sample in the cup, with distilled water on the upper surface and a certain humid environment at the lower surface of the sample. When the distilled water permeates through the sample and into the humid environment, water vapor transmission rate can be obtained by measuring cup weight at intervals. 
Though rarely applied, inverted cup method is not new to the industry. The term, inverted cup method, states once ASTM E96, Standard Test Methods for Water Vapor Transmission of Materials. In GB 1037, Test Method for Water Vapor Transmission of Plastic Film and Sheet—Cup, the Chinese adoption of ASTM E96, only the desiccant method is introduced. Thus, there is not proper attention on inverted cup method domestically. Now, with increasing demands and international trading, testing demands for inverted cup method has found gradual increase. Unfortunately, the existing instrumental structure of weighing method cannot completely satisfy the needs for inverted cup method testing, especially in the process of cup inversion and the structure of the cup. Such needs has been taken into consideration in the design of Labthink PERME W3/031 Water Vapor Transmission Rate System; the testing of inverted cup method can be realized with customized cup. At the same time, this instrument can realize water method testing with certain functional expansions. 

4.More Powerful SoftwarePermeability test is more sensitive to data produced in process, which sets high requirements for software performance. Otherwise, data accuracy would be seriously affected. Labthink world leading software for permeability testing, based on its complete functions and convenient operation, can provide complete and rapid whole course monitoring, as well as innovations in authority setting and testing process recording. Meanwhile, language selection and operational help have been improved. 

5.ConclusionsWeighing method is widely applied as the basic testing method for water vapor transmission rate. As a result, every technological innovation of weighing method tester would bring great influence to the whole industry. Now, the new patented structure of Labthink weighing method instrument has accomplished a thorough upgrading in testing efficiency, testing accuracy and functional extensions, which make it more outstanding when compared with various kinds of sensor method water vapor transmission rate testing instruments so as to help customers’ purchase objectively and scientifically.

Labthink - Permeation Testing Instruments

Labthink focusing on the laboratory testing instruments R&D and production and laboratory IT services, is dedicated to provide professional quality control solutions for customers in packaging, food, pharmaceutical, medical, daily chemistry, printing, adhesive, automotive, petrochemistry, bioscience, construction, new energy and other industries.

Labthink, as a knowledge-based enterprise, advocates scientific research and integrates production-manufacturing with IT services. Labthink is devoted to share excellent testing technologies and advanced IT achievements with customers worldwide. Labthink instruments are now operating in more than 5000 laboratories of authoritative institutions and renowned enterprises. Labthink IT services, with the innovative mode of cloud computing online information management, actively promotes the information trends of Laboratories!

Labthink, the excellent supplier of permeation testing instruments and testing services!