Since its birth, lithium-ion batteries have seen little change in their basic structure. Now all lithium-ion battery architectures are based on Sony's sandwich structure designed this year. The battery consists mainly of positive and negative foils, in order to prevent short circuits between the positive and negative electrodes. A layer of porous polymer membrane is needed between the positive and negative pole pieces to move Li+ through the diaphragm between the positive and negative poles. This structural design can be said to be so good that it has been more than 20 years. The structure of the ion battery has not undergone major changes, but this structure actually has many problems, and the first is the safety issue. The polymer separator has a relatively low melting point, resulting in a large amount of heat generation or internal short circuit in the battery due to electric abuse or mechanical abuse. At the time, the diaphragm will shrink and melt under the effect of high temperature, leading to direct contact between the positive and negative electrodes, causing terrible consequences - thermal runaway.
In addition, the traditional structure of lithium-ion batteries in the energy density, especially the volume energy density there is a great disadvantage. In the lithium-ion battery can store energy only positive and negative active material, but the traditional production process and the battery structure makes lithium There are a large number of non-active materials in the interior of the ion battery - Al foil, Cu foil and separator, and a large amount of unused space (between the electrode and the diaphragm, between the battery core and the housing, etc.), which greatly reduces The lithium ion battery volume energy density and weight energy density.
The problems caused by the design ultimately need to be solved from the design point of view. Enovix engineers have found inspiration from the semiconductor industry to solve this problem. In the past decades, the semiconductor industry has developed rapidly under the drive of Moore's Law. In 18 months, the number of transistors on a chip doubled. In 1965, when Dr. Gordon Moore made this prediction, the number of transistors that can be integrated on a single chip is only 30. Today, every chip is integrated. Billions of transistors. Looking back at the history of lithium-ion batteries, the energy density has only increased about 5% per year over the past two decades, and the demand for energy storage from electronic devices has increased dramatically. In the era of mobile phones, the mobile phone was charged once a week, and charging in the era of smart machines became a necessary daily lesson.
Fortunately, the cornerstone Si material for the semiconductor industry is also a very good anode material for lithium-ion batteries. One Si can combine with 4.4 Li to form Li4.4Si, and 6 C can combine with 1 Li to form LiC6. Therefore, the theoretical capacity of graphite anode is only 372mAh/g, while the theoretical capacity of Si material can reach more than 4200mAh/g, which makes Si material an ideal anode material, so the mature Si material processing technology in the semiconductor industry is expected to be applied. In the lithium-ion battery industry.
Enovix's three founders, Lahiri, Shah, and Dales all have experience in semiconductor design and packaging and testing, so they combined the photolithography process in the semiconductor industry with a Si negative-electrode Li-ion battery and photolithography on a Si substrate. The process design a 3D solid-state lithium-ion battery (process shown below), the process mainly includes the following steps: 1) The first step is to draw a pattern on the surface of the silicon wafer coated with photoresist; 2) Corrosion is performed, leaving a portion as a negative electrode of Si, and a part of it is required as a positive electrode current collector support structure; 3) Electroplating a thin metal layer on the remaining Si negative electrode and positive electrode current collector support structure as a current collector; A layer of ceramic separator is deposited on the surface of the negative electrode of Si; 5) The remaining space filled with the positive electrode material is prepared. The Si substrate prepared to complete the lithium ion battery will be laser-cut into a single-cell battery. These single-cell batteries are first welded to the positive electrode. The negative lead, and then drying, these last 1mm thick single-cell batteries will be stacked according to the needs of different thickness and shape of the battery.
This technology greatly improves the space utilization of lithium-ion batteries. 75% of the space developed by Enovix can be used to store batteries. The volumetric energy density is 1.5-3 times that of conventional lithium-ion batteries. This is for consumption. Electronic products are undoubtedly of great attraction.
Another big advantage of Enovix batteries is their safety. The polymer diaphragms used in traditional lithium-ion batteries can melt and contract at high temperatures, causing thermal runaway of lithium-ion batteries. The ceramic diaphragms used in Enovix batteries have largely avoided this. The problem. Even if the battery is short-circuited, the distributed microelectrode structure of the Enovix integrated battery can also limit the propagation of current and heat, thus further enhancing the safety of the battery. Put a 130mAh traditional lithium-ion battery and a 100mAh Enovix. The batteries were all charged to 250% SoC, and then acupuncture experiments were performed. The conventional structure of lithium-ion batteries had a thermal runaway and caught fire, while Enovix did not experience thermal runaway, fully demonstrating the safety of Enovix batteries.
For lithium-ion batteries, the cost is often the biggest enemy. Applying the technology of the semiconductor industry to lithium-ion batteries first needs to be solved and how to reduce costs. Cypress Semiconductor has helped its subsidiary SunPOwer to produce high-performance solar energy at a very low cost. Batteries, with the help of Cypress Semiconductor, Intel Capital and Qualcomm Investment, Enovix began to use SunPower's mature technology to improve its production process in 2014, which will significantly reduce production costs.
The existing lithium-ion battery structure is based on Sony's tape production process. Its structure has limited the increase in volume energy density and weight energy density of lithium-ion batteries. The 3D Si battery process developed by Enovix is based on semiconductors. On the basis of industry, the battery solves the problems of low space utilization and safety issues of the traditional structure of lithium-ion batteries. With the maturity of the process and the continuous reduction of costs, it is expected to bring revolutionary changes to the lithium-ion battery industry!
