Many battery companies have created sexy names for new products, such as "4680", "top current", "M3P", "Short knife", "condensed State", to create a memory point rich in individual characteristics and easy to spread, and strive to make it familiar to users from the main engine factory to the C-end.
If we put aside these names and let the battery return to its original nature, we can dig the depth and breadth of the discovery of new materials, the improvement of performance and the innovation of products that are easily unimaginable, and we will see the real bottom of the iceberg world.
In this bottom world, a variety of complex physical, chemical, and electrochemical processes are intertwined like mysterious ice caves. Only through in-depth basic research and the use of reasonable detection means can we gradually uncover these mysteries, understand the microscopic mechanism inside the battery, and discover the potential and possibilities.
Battery companies want to perform well on these key factors, which requires quality control methods that exceed those of their peers. First of all, in the research and development process, fully understand and control the characteristics of battery-related materials, and choose good materials.
The high safety, high energy density, high rate performance, durability and lower cost of power battery products are the key factors to determine whether they can achieve market success. The comprehensive upgrade of competitive play means a comprehensive upgrade in the three aspects of "performance", "security" and "cost".
Excellent batteries cannot be separated from more efficient tools
Materials fundamentally determine battery performance. Improving battery performance by improving materials, optimizing battery aging mechanism, applying new materials and changing cell structure are the main directions of cell research and development 。For example, in terms of material system, new material systems (high nickel positive electrode, silicon based negative electrode, lithium metal negative electrode, solid electrolyte, etc.) are used to improve the energy density of monomers; Or develop lithium ferromanganese phosphate, explore the commercial application of sodium ion batteries, reduce costs; Or speed up the research and development process of solid-state batteries, so that the battery performance is higher and more durable. In terms of cell shape, square batteries, especially LFP short knives, have become one of the preferred solutions for mainstream enterprises, taking into account performance, integration and manufacturing; Large cylindrical batteries are also a hot direction, and Tesla and BMW have put forward specific implementation plans. In terms of fast charge technology, many Oems began to introduce 800V high voltage platforms, And joint battery companies to launch 2C~4C fast charge scheme.
The modification of materials, the development of new materials, and the design of cell structure often combine multiple strategies to promote the upgrading and innovation of batteries.
For example, from 2020 to the present, Tesla has opened the bureau and domestic battery companies have jointly promoted it The large cylinder battery has a very unique killer：
1.Due to the use of steel shell cylindrical shell and directional pressure relief technology, the binding force of the battery itself is relatively uniform, effectively inhibit expansion, and provide the first layer of strong protection for the overall safety of the battery pack. This also makes the exploration of large cylinder batteries more daring in materials, and the mainstream materials under the current high specific energy route, High-nickel ternary anode materials and silicon-based anode materials have become more widely used in large cylindrical batteries.
2.All-pole ear design, the battery directly from the positive/negative collector current, doubling the current conduction area, shorten the current conduction distance, thereby greatly reducing the battery internal resistance, improve the peak power of charge and discharge.
For lower cost ferromanganese lithium battery system，The M3P battery of the Ningde era will be installed in Tesla's domestic Model 3 model in the third quarter. The network has continuously reported that the M3P battery is the LFMP lithium manganese iron phosphate battery. Ningde Times said in its research that M3P is not precisely lithium ferromangmanganese phosphate, but also contains other metallic elements - which the company calls "the ternary of the phosphate system."
At the globalization strategy conference on August 10, the company pointed out that its LFMP took the lead in realizing the mass supply of 73 products (manganese-iron ratio), and based on this, promoted LFMP and the term-based composite product M6P and the next generation of process products. They believe that by 2030, generalized ternary materials and phosphates will still dominate, The high nickel material in ternary, the iron manganese lithium in phosphate and the sodium electricity will usher in very rapid growth.
On the other hand，The industry also needs to support higher power batteries. This requires battery companies to strengthen battery thermal management at the same time, but also from the battery materials (especially the selection of negative electrode materials and microstructure design), electrode design, battery shape, etc., to reduce internal resistance and strengthen heat dissipation. Improve battery rate performance.
At present, many companies have launched fast charging battery solutions. Xinwang Da in this year's Shanghai Auto Show focused on the launch of its flash battery, the deployment of proprietary technology in the core materials, self-designed flash silicon material technology, high safety nickel anode and new silicon based system electrolyte technology and other key technologies. Support electric vehicles can be charged from 20% to 80%SOC in 10 minutes, making charging as fast as refueling.
As the so-called "work to do good, must first strengthen its tool", better power battery products can not be separated from more efficient and powerful testing tools.
Microstructure characterization of materials is the key to cell research and development. At present, many materials characterization methods have been introduced and widely used.
In the development process, engineers use optical microscopes, X-ray microscopes, and 3D inspection to observe electrode materials, detect electrode defects, and analyze battery failure principles. It can also observe the particle size of the material, the ratio and distribution of various components, etc., to deepen the knowledge and understanding of research and development personnel. These can improve the battery performance while improving the research and development efficiency, and then provide a basis for the improvement of materials and processes.
Two-dimensional microscopic imaging and characterization of battery materials
The light microscope, which uses optical principles to magnify objects, was first formed in the 17th century. The resolution of the optical microscope is related to the wavelength of visible light (390~780nm), and its maximum magnification can reach more than 1000 times, achieving micron level resolution, which is widely used in life science, materials science and other fields.
In the research and development of power batteries, the optical microscope can be used to observe the electrode structure, detect electrode defects, analyze the failure principle of the battery, observe the growth behavior of lithium dendrites, etc., and then provide a basis for the improvement of materials and processes.
However, due to the wavelength of visible light, the magnification of the optical microscope is limited, and the observation of more microscopic structures cannot be achieved, and the electron microscope is a good solution to this problem.
The electron microscope was first invented by the British physicist Lucas in 1931, using an electron beam instead of a light beam, the maximum magnification can reach 3 million times, to achieve nanoscale resolution.
Due to the higher resolution of the electron microscope, multi-dimensional information (composition, characterization information, particle size, proportion of ingredients, etc.) can be obtained in battery development with different probes. To realize the detection of positive and negative electrode materials, conductive agents, binders and membranes and other microstructures (observing the morphology, distribution state, particle size, existing defects, etc.).
Scanning electron microscopy (SEM) is commonly used to observe the surface morphology of samples. Due to its high resolution, SEM can clearly reflect and record the surface topography characteristics of materials, so it has become one of the most convenient means to characterize the morphology of materials.
Combined with argon ion polishing technology (also known as CP cross-section polishing technology), SEM can complete the observation and analysis of the internal structure of the sample. This is also the most effective sample preparation method for preparing the electrode slice cross-section of lithium battery material.
SEM can also be used to observe the cyclic aging of battery particles. At present, through analysis, it is found that particle fragmentation characterization has become the breakthrough point for scholars to improve the properties of cathode materials.
Battery detection: From 2D to 3D
Traditional detection methods are usually limited to the 2D plane, but 2D images will have local deviations (for example, when preparing the sample just cut to the right part of the problem). 3D images can better characterize the material structure, make the detection results more intuitive, and help to deepen the knowledge and understanding of researchers. Improve research and development efficiency and better improve battery performance.
Without disassembling the battery, the X-ray microscope can carry out high-resolution imaging of specific areas inside the battery, achieve 3D non-destructive imaging of the sample, distinguish the electrode particles from the pores, the diaphragm from the air, etc., which can greatly simplify the process and save time.
High-resolution micro-CT can realize the three-dimensional visualization of the internal structure of the battery, solve the problems such as secondary damage to the internal structure caused by disassembly and other reasons, and clearly show the real situation inside the battery. Here, X-ray microscopy is applied.
At present, the accuracy of CT imaging has entered the sub-micron stage, and the battery materials and pores can be analyzed and detected.
On the basis of X-ray microscopy, Zeiss introduced a method for characterizing the evolution of microscopic structures that can change with time (4D). With true nanoscale 3D X-ray imaging with spatial resolution up to 50nm and voxel sizes down to 16nm, more information can be obtained and even finer details can be identified.
Currently, X-ray microscopes can achieve resolutions up to 50nm, and when higher resolution details are needed, a new generation of focused ion beam (FIB) technology is needed. FIB uses high-intensity focused ion beams (usually gallium ions) to nano-process materials, combined with scanning electron microscopy (SEM), The sample can be processed and observed at the same time.
Currently, both Zeiss and Thermo Feld have introduced focused ion beam microscopes.
The Zeiss Crossbeam series combines the imaging and analytical performance of high-resolution field emission scanning electron Microscopy (FESEM) with the processing capabilities of FIB, whether for multi-user experimental platforms or research or industrial laboratories, with the modular platform design concept of the Crossbeam series. The instrument system can be upgraded at any time based on its own needs (for example, large-scale material processing using Laser+FIB). In processing, imaging or 3D reconstruction analysis, the Crossbeam series will greatly improve the efficiency of FIB applications.
When it is necessary to analyze the distribution of various components, need to simulate, and need to see the internal structure, FIB can rely on low-voltage imaging, can scan more 3D details, and can do a variety of tests, so that the research and development work is more effective.
In situ testing of batteries and multi-technology correlation applications
Whether it is light microscopy, electron microscopy, X-ray microscopy and industrial CT, different test methods have their advantages and are suitable for different scenarios. However, a single detection method often cannot fully characterize the material properties. Therefore, the industry will use different test equipment together, To realize the correlation of multiple means, multi-dimensional information can be obtained in the test, so that the result is more intuitive.
In the early days, the starting point of multi-means association was to observe the needs of the tested object at different resolutions. For example, CT and X-ray microscopy can be nondestructive detection, but the resolution is relatively low, so that the initial look at the material, you can use both to first look at the morphological characteristics. Scanning electron microscopy has a higher resolution, For example, Zeiss introduced FIB-SEM products based on scanning electron microscopy, which can achieve 3D imaging with high resolution (3nm). In this way, by using CT→ X-ray microscope → FIB-SEM, the selected area is amplified step by step, more comprehensive and accurate information can be obtained, and rapid positioning can be achieved. Make the detection more efficient.
The electron microscope is provided with multiple expansion ports to add different probes. However, in battery development, the SE, BSE and EDX detectors equipped are not enough to fully characterize the properties of the material. Especially in the case of large sample sizes, it is not easy to focus on the same specific particle. Raman probes can help analyze molecular structure and composition, interface structure and so on. But in general, Raman electron microscopes are separate and independent. Therefore, if you can use BSE, EDS and Raman to take overlapping information of three images on the same test object, you can achieve multi-angle analysis in situ.
Microscope manufacturers are doing just that. For example, Germany WITec, Czech Tescan, Zeiss and so on launched the RISE system, which can realize the joint application of Raman imaging and SEM technology. By combining the battery surface morphology (SEM) and element distribution (EDS) with the electrode material molecular composition information (Raman spectrum), the in-situ multi-angle analysis of the material can be realized to understand the state of the battery and the morphology, element and molecular composition of the material at different locations, so as to evaluate the battery performance.
Material testing usually accompanies the sample preparation process, and since FIB-SEM requires multiple sample preparation tests on the same sample to build a 3D image, conventional sample preparation methods can take a long time. To solve this problem, Zeiss came up with a very clever set of joint solutions.
First, Versa can be used to obtain 3D images with a large field of view and find suspicious locations without loss.
Then, for more in-depth analysis of the suspect location, it is necessary to cut to the specified location. Fs-laser femtosecond laser can achieve a high rate of sample cutting (107μm3/sec), rapid rough sampling, rapid completion of deep sample analysis, At the same time, the high performance and high resolution of FIB-SEM are not affected.
Finally, it is finely polished with FIB and photographed for analysis.
Through the joint application of Versa, FIB-SEM and Fs-laser, rapid location and sample preparation of test objects are realized, making detection simpler and faster, and helping R&D personnel improve work efficiency.
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