At the auto show, a colleague went to visit BYD's booth, and came back with a message. The colleague in charge of the battery called me and asked about the two-way inverter charging and discharging technology. Sometimes I really can't stand this kind of hype company, your sister's, charging content, the future is to develop standard open content as an OEM manufacturer, it is necessary for Grid and OEM to work together to promote, you have a broken interface What protocol is used to administer energy to the grid!
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First of all, I have to explain that the charging conference I attended can probably keep up with the current charging communication standard (ISO 15118).
ISO 15118 > Road vehicles – Communication protocol between electric vehicles and grid
ISO 15118-1 > Part 1: Definitions and use-cases
ISO 15118-2 > Part 2: Sequence diagrams and communication layers
ISO 15118-3 > Part 3: PLC Technology and Timings
What's more, for the harmonics caused by distributed power supplies, in fact, we want to do a high-power inverter with the corresponding power quality. The Toyota 1.55 is not worthwhile. .
SAE Power Quality Standards, - J2894 Part 1 – Target parameters – in draft
SAE Power Quality Standards, - J2894 Part 2 – Testing Procedures – pending
What's more, the life of the battery is actually very restrictive, and there is a little learning in this area.
I have some knowledge of the battery in my brain. I saw an article "Overview of the Power Battery Failure Mode" is good, and I will do some supplements on it. Here first list the reasons for the capacity loss. The more you know about the battery, you will find that lithium-ion batteries do not learn electrochemical and process common sense, there is no way to understand and do a good job in battery system.
1. Formation of the interface film
“Due to the irreversible reaction between lithium ion or electrolyte and the electrode, a solid electrolyte interface layer (SEI) is formed at the interface between the negative electrode and the electrolyte. Lithium ions lost due to the formation of such a passivation film will result in a capacity between the two electrodes. The change in balance will cause the battery capacity to drop during the first few cycles."
I started to look at this SEI thing. I really didn't understand it. I slowly read some materials and I got a little understanding. A classic article, see "A reiview of the features and analyses of the solid electrolyte interphase in Li-ion batteries", Battery performance, irreversible charge "loss", rate capability, cyclability, exfoliation of graphite and safety are dependent On the quality of the SEI.
2. Phase change of the cathode material
There are two types of phase transitions in lithium-ion batteries: one is the phase change of the electrode material during the normal deintercalation of lithium ions; the other is the phase change of the electrode material during overcharge or overdischarge.
For the first type of phase transition, it is generally believed that the normal deintercalation reaction of lithium ions is always accompanied by a change in the molar volume of the host structure, and at the same time, stress is generated inside the material, thereby causing changes in the host lattice, and these changes reduce interparticles and particles. Electrochemical contact with the electrodes.
The second type of phase change is the Jahn-Teller effect. The Jahn-Teller effect refers to the expansion and contraction of the structure caused by repeated insertion and deintercalation of lithium ions, which causes the oxygen octahedron to deviate from the spherical symmetry and become a deformed octahedron configuration. The irreversible transformation of the spinel structure due to the Jahn-Teller effect is also one of the main reasons for the capacity decay of LiMn2O4. In the deep discharge, the average valence of Mn is lower than 3.5 V, and the structure of the spinel is changed from a cubic phase to a tetragonal phase. The tetragonal crystal has low symmetry and strong disorder, which makes the reversible reversibility of lithium ions decrease, which is manifested by the reversible capacity of the positive electrode material.
3. Reduction of electrolyte
Electrolytes commonly used in lithium ion batteries mainly include a solvent composed of a mixture of various organic carbonates (such as PC, EC, DMC, DEC, etc.) and an electrolyte composed of a lithium salt (such as LiPF6, LiClO4, LiAsF6, etc.). Under charging conditions, the electrolyte is unstable to the carbon-containing electrode, so a reduction reaction occurs. Electrolyte reduction consumes electrolytes and their solvents, which adversely affects battery capacity and cycle life. The resulting gases increase the internal pressure of the battery and pose a threat to system safety.
The above two calculations affect Cycle Life at the same time, and the second item may be more direct. After 10 years of technology, you have to look at the performance and life of the battery to see, can come out to operate at the auto show, it is impossible to imagine.
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