New materials break through the bottleneck of lithium batteries -Lithium - Ion Battery Equipment
Scientists have been actively looking for new ways to shorten the charging time of electric vehicles. Recently, the team of Academician Yu Shuhong from the University of Science and Technology of my country, in cooperation with the team of Professors Yao Hongbin and Ni Yong, is committed to solving the contradiction between high energy density and fast charging performance of lithium batteries, and has proposed and prepared a new type of double gradient graphite anode material. The lithium battery charges to 60% in 6 minutes. The results were recently published in Science Advances.(Lithium - Ion Battery Equipment)
High energy density and fast charging performance are a pair of contradictions. Currently, electric vehicles powered by lithium batteries are favored by people because of their energy saving and environmental protection. However, the charging time of electric vehicles is much longer than that of traditional fuel vehicles, which greatly reduces the user experience.
"This is mainly because the poor rate performance of the graphite negative electrode in lithium batteries limits the fast charging capability of electric vehicles." Lu Leilei, the co-first author of the paper and a special associate researcher at the Hefei National Research Center for Microscale Matter Science, University of Science and Technology of my country Explain to "my country Science Journal".
Energy density and power density are two important parameters for evaluating battery systems. Energy density determines the amount of energy that can be stored per unit mass/volume, while power density determines the rate of charge and discharge of the battery. Ideally, the higher these two parameters, the better the performance of the lithium battery. However, high energy density and fast charging performance are a pair of contradictions, and it is a process of "one after another".
Lu Leilei said, "High energy density usually means that the active material loading of the battery cell is relatively high, and the electrode is relatively thick, so it has a long lithium ion transmission path and limits the charge and discharge rate."
Therefore, in order to improve the rate performance of graphite anodes, the traditional strategy is to make the graphite electrodes porous or thin. "However, these methods often sacrifice the energy density of the prepared batteries." Lu Leilei said frankly.
Is there a solution that can achieve both high energy density and fast charging performance "fish and bear's paw"? Yu Shuhong's team decided to start with designing the electrode structure to improve the fast charging performance of lithium batteries while ensuring energy density.
"Queue" graphite particles to speed up charging
The research team first constructed a new particle-level theoretical model to simultaneously optimize the two parameters of particle size distribution and electrode porosity distribution in the electrode structure to improve the fast charging performance of graphite anodes.
According to Lu Leilei, the traditional two-dimensional model usually simplifies the particles into a homogeneous spherical shape and uniform distribution of pores. In fact, graphite particles are mostly of different sizes and shapes, usually in a fairly random order. At the same time, the shape and size of the pores are also non-uniformly distributed.
The new particle-level theoretical model is a three-dimensional model constructed based on real graphite particles, which is very close to the actual electrode structure.
In the particle-scale theoretical model, the researchers re-"lined up" the graphite particles in order of size, while adjusting the electrode porosity size distribution. Specifically, the graphite particles closer to the top of the cell are smaller and have higher porosity, and the particles closer to the bottom are larger and have lower porosity.
"We call this structure a double gradient electrode." Lu Leilei said, the simulation results show that under the condition of high current density charging, this new structure is related to traditional random homogeneous electrodes and single gradient electrodes, showing Excellent fast charging performance.
The ideal structural model has been found, and the next step is how to implement it in the electrode.
In the traditional electrode preparation method, due to the high viscosity of the slurry, the prepared graphite slurry is stable and does not easily settle. Therefore, the prepared electrodes, including graphite particle size and porosity size, are usually uniformly distributed. Lu Leilei said, "Just like instant milk powder, any part is homogeneous."
High energy density and fast charging performance are a pair of contradictions. Currently, electric vehicles powered by lithium batteries are favored by people because of their energy saving and environmental protection. However, the charging time of electric vehicles is much longer than that of traditional fuel vehicles, which greatly reduces the user experience.
"This is mainly because the poor rate performance of the graphite negative electrode in lithium batteries limits the fast charging capability of electric vehicles." Lu Leilei, the co-first author of the paper and a special associate researcher at the Hefei National Research Center for Microscale Matter Science, University of Science and Technology of my country Explain to "my country Science Journal".
Energy density and power density are two important parameters for evaluating battery systems. Energy density determines the amount of energy that can be stored per unit mass/volume, while power density determines the rate of charge and discharge of the battery. Ideally, the higher these two parameters, the better the performance of the lithium battery. However, high energy density and fast charging performance are a pair of contradictions, and it is a process of "one after another".
Lu Leilei said, "High energy density usually means that the active material loading of the battery cell is relatively high, and the electrode is relatively thick, so it has a long lithium ion transmission path and limits the charge and discharge rate."
Therefore, in order to improve the rate performance of graphite anodes, the traditional strategy is to make the graphite electrodes porous or thin. "However, these methods often sacrifice the energy density of the prepared batteries." Lu Leilei said frankly.
Is there a solution that can achieve both high energy density and fast charging performance "fish and bear's paw"? Yu Shuhong's team decided to start with designing the electrode structure to improve the fast charging performance of lithium batteries while ensuring energy density.
"Queue" graphite particles to speed up charging
The research team first constructed a new particle-level theoretical model to simultaneously optimize the two parameters of particle size distribution and electrode porosity distribution in the electrode structure to improve the fast charging performance of graphite anodes.
According to Lu Leilei, the traditional two-dimensional model usually simplifies the particles into a homogeneous spherical shape and uniform distribution of pores. In fact, graphite particles are mostly of different sizes and shapes, usually in a fairly random order. At the same time, the shape and size of the pores are also non-uniformly distributed.
The new particle-level theoretical model is a three-dimensional model constructed based on real graphite particles, which is very close to the actual electrode structure.
In the particle-scale theoretical model, the researchers re-"lined up" the graphite particles in order of size, while adjusting the electrode porosity size distribution. Specifically, the graphite particles closer to the top of the cell are smaller and have higher porosity, and the particles closer to the bottom are larger and have lower porosity.
"We call this structure a double gradient electrode." Lu Leilei said, the simulation results show that under the condition of high current density charging, this new structure is related to traditional random homogeneous electrodes and single gradient electrodes, showing Excellent fast charging performance.
The ideal structural model has been found, and the next step is how to implement it in the electrode.
In the traditional electrode preparation method, due to the high viscosity of the slurry, the prepared graphite slurry is stable and does not easily settle. Therefore, the prepared electrodes, including graphite particle size and porosity size, are usually uniformly distributed. Lu Leilei said, "Just like instant milk powder, any part is homogeneous."
