Today, the battery has become the core of the decision to determine the future of electric vehicles, it is not difficult to understand so many battery manufacturers in the battery technology brains, expect a major breakthrough, and develop a variety of ambitious development goals, The battery density of the battery system from 250Wh / L or so to 500Wh / L, while significantly reducing production costs.On the one hand, the battery material needs to be further optimized to improve the battery energy density, on the other hand, the battery space body needs to improve, In the case of non-active materials in a limited space, the existing battery pack package resulted in a large volume of non-battery active material occupied and could not take full advantage of the limited battery space. To achieve this goal, IAV and Thyssenkrupp AG and Fraunhofer Institute for Ceramic Technologies and Systems (IKTS) work together to develop the chassis-embedded energy (EMBATT: chassis-embedded energy), directly into the battery chassis, significantly reduce the volume of the structure of the battery itself, to improve the energy density Wh / L goal. EMBATT concept of the central idea is to use bipolar b ipolar lithium ion battery. In this collaborative development project, IAV is mainly responsible for vehicle development, including vehicle concept, measurement safety, battery layout and design, control software calibration. IKTS is responsible for customization of battery materials and electrodes manufacturing and processing technology. Thyssenkrupp AG Mainly responsible for the late battery production.
Based on the EMBATT concept of bipolar batteries to achieve the following objectives:
• Significantly reduce system complexity and increase battery density to 500 Wh / L
· Reduce internal resistance and reduce cooling requirements
The use of fewer parts, manufacturing costs can be reduced
· Meet vehicle safety requirements
· Advanced battery material to further improve the energy density
The current lithium-ion battery will be wound or laminated after the electrode into the shell (cylindrical, square, or soft package), and then with other structural parts, electronic devices, management unit integrated into the battery system that. Body battery to the battery system, due to the presence of a large number of non-active substances (structural parts, electronic components, wiring harness, etc.), energy density loss of up to 40-60% (or even higher), the current battery system energy density roughly 120-300Wh / L (not Wh / kg here).
The EMBATT project's battery development goal is to break the boundaries of traditional batteries and modules, integrate bipolar electrode-made batteries into the chassis, and achieve a large battery voltage configuration of 850-1200V (approximately 2) depending on the size of the package Square meters of the battery), making it possible to drive a mileage of 1000 km One of the challenges of this development project is how to produce bipolar electrodes because it requires two different electrodes on both sides of the electrode Of the material, the minimum battery cell thickness of about 300 microns, which is a more complex preparation process.The mechanical stability of the battery through the internal and external support structure to achieve.
In addition to the special design of these battery structures, another focus is on the use of high-efficiency battery materials. EMBATT project in the anode material currently selected lithium titanate LTO, positive selection of lithium manganese oxide LNMO, single cell voltage In the 3.2V or so (select other materials can also, but the voltage will be lower), the next important material is to select the appropriate electrolyte, from the traditional liquid electrolyte to the solid electrolyte are within the scope of the test, long-term, all solid Electrolyte will be the ultimate choice, one of the diaphragm options is a ceramic diaphragm, which helps to integrate the solution and membrane of the solid electrolyte.The EMBATT project in the bipolar electrode on both sides of the current are coated with LTO (The other cathode material can also be.) First, the first bipolar electrode with a laser cutting the first pre-cut, and then in the second punch to get the final electrode size. The polar electrode pads are stacked to form a series connection between the battery cells. According to the progress of the project, the 1000 km electric car based on the EMBATT concept is expected to be released in 2025.
According to IKTS, the EMBATT project concept comes from the solid oxide fuel cell SOFC stack structure design. In the project, IKTS is mainly responsible for: battery cell design concept research; development / optimization of battery active materials, as well as ceramic diaphragm and electrolysis Liquid; battery unit manufacturing process development.
At present, IKTS and cooperation agencies have completed the development of EMBATT1.0 and EMBATT2.0 1.0 and 2.0, the most important change is that the cathode material from the 1.0 project in the NCM or LFP upgrade to LNMO, using a metal element Doped spinel lithium manganate, increased the upper limit voltage. Diaphragm, liquid electrolyte upgraded to the all solid electrolyte, which will be more conducive to the production of battery cells. 1.0 and 2.0, respectively, the energy density of 200Wh / L and 450Wh / L , Which has no advantage over the energy density of the current power cell, and may have some advantages over the battery system in the future, but now that the battery prepared by the bipolar electrode has not yet been embedded on the chassis, the battery system level Of the energy density advantage is not clear.Therefore in the EMBATT 3.0, the negative made a great change, the use of metal lithium as a negative, and the use of glass-ceramic all solid electrolyte, the collector is no longer confined to aluminum (present It is not clear the specific material of the fluid), through these optimizations to achieve 800Wh / L energy density target.
In the manufacturing process, 1.0 and 2.0 of the manufacturing process and the current lithium-ion battery manufacturing process is no significant difference in 3.0, due to the use of all solid glass ceramic electrolyte, so the electrode and electrolyte assembly can be completed in the same step, But the subsequent increase in the heat treatment links, mainly in order to make the electrode and solid electrolyte interface better contact. This 3.0 project, the whole solid electrolyte development, electrolyte and electrode interface compatibility issues are focused on the content of the study, This is consistent with the general research on solid-state batteries.
In general, the biggest feature of EMBATT is not its material innovation, because these materials research and innovation has always been a hot topic in the field of lithium-ion battery, EMBATT interesting place is the bipolar electrode prepared by the battery directly integrated into the car The concept of the chassis, and the concept of this extension in the manufacturing process improvement. Interestingly, at this year's Shanghai auto show, auto parts supplier - Bentler proposed independent design and development of new energy vehicle chassis system , One of the goals of the chassis system is to achieve chassis integration or modular integration, the battery is also considered integrated into the chassis of one of the parts.In addition, this year's ninth global automotive industry summit, similar to the electric chassis The platform has also been repeatedly stressed.Thus, this platform will become the development of the trend of electric vehicles.
The concept of bipolar electrodes has been a long time, the application of lithium-ion batteries for a long time, has not been a large-scale application. The following figure compared to the traditional lithium-ion battery (a) and bipolar lithium battery (b Figure 1 shows a case where each cell unit includes a positive electrode (typically coated on an Al substrate), a negative electrode (typically coated on a Cu substrate), and b , The battery cell unit cell also includes a positive electrode and a negative electrode, but the positive electrode and the negative electrode active material share a substrate. When two battery cells are connected in series, the side of the bipolar electrode is in the current cell cell as the negative electrode and the other One side is used as a positive electrode in adjacent cell cells.
The study of bipolar electrodes has occurred as early as two or three decades, for example, in the 1990s, Yardney Technologies has conducted a study on bipolar lithium-ion batteries. The design minimizes the resistance between adjacent cells in the cell cell cell stack, resulting in a more uniform distribution of current and potential on the surface of the positive and negative active coating of each bipolar cell cell. The cell of the polar cell has a higher power characteristic. Fig. 1 is a typical bipolar lithium ion battery section consisting of a plurality of bipolar battery cells. Fig. 2 is a bipolar battery 16a, 16b, ..., 16n are the negative side of the battery cell; 18a, 18b, ..., 18n are the battery cells; 14a, 14b, ..., 14n are the positive side of the battery cell; 20b, 20c, ..., 20n are collectors (e.g., 14a and 16b in Fig. 2 share a current collector), and the current collector may be coated with a bimetallic substrate, for example, Cu-Al bimetallic, negative electrode active material Cu side, the positive electrode active material is coated on the Al side, and 24 is the negative electrode active 26a is a positive electrode active material; 28a, 28b, ..., 28n are insulating connection fixing structures, each bipolar electrode is fixed by the connecting structure. In Fig1. and Fig. 2, there are n-1 bipolar electrodes (The positive electrode and the negative electrode active material on both sides of the current collector), the uppermost layer 20a has only one side of the negative electrode and the other side is connected to the negative electrode pole 29, and the lowermost layer 20n + 1 has only one side of the positive electrode and the other side Connected.
Figure 3 is a bipolar electrode stack stack, can be called the stack 40. Among them, 32 is the diaphragm; 34 is the collector; 36 is a bipolar electrode, both sides are positive and negative active material. The basic structure and the above The example is the same.
The following figure is a CR2032 button cell with three bipolar electrodes. The positive electrode is LFP and the negative electrode is metal lithium, using quasi-solid polymer electrolyte and stainless steel current collector. As can be seen from the voltage curve, as long as the bipolar electrode the number of units can change the voltage of the battery, here are given 1unit, 2units, 3units voltage curve.For example, it is easy through 5 bipolar unit to achieve a 12V lithium-ion battery, the figure on the right is Japan A part of the cross section of a 12V bipolar battery from Toshiba can be seen from the parameters in Table 1. The cathode material is LiMn0.85Fe0.1Mg0.05PO4, the anode material is LTO, the current collector is Al, the solid electrolyte electrolyte is Li7La3Zr2O12 (LLZ) and PAN. From the packaging point of view, laminated flexible packaging is more suitable for a bipolar battery in a way.
From the above structure and data point of view, the use of bipolar electrode structure, it is easy to achieve high battery voltage, which is more than by the number of batteries in order to achieve high voltage method to be more efficient: to reduce the battery ineffective Space, reducing the connection resistance.Compared with the development of high-voltage cathode materials in the slow progress, bipolar electrode may be a possible more efficient way to achieve the battery high voltage output.Of course, as mentioned earlier , The real practical application also need to solve a lot of manufacturing problems.We think of our country in 2016 issued electric vehicle technology line, pure electric vehicle battery system energy density target is 500Wh / L (2025), 700Wh / L (2030), perhaps, the use of chassis embedded battery technology is likely to be one of the ways to achieve this goal.
