Literature Appreciation: Application Analysis of Silicon Anode in High Energy Density Lithium-ion Battery

1.Author Information and Article Summary

In 2017, the Jaephil Cho team summarized several problems faced by the application of silicon anode in the high-energy lithium-ion battery. In order to improve the volume and energy density of the battery, the impact on electrochemical performance from the cell system design, and focused on the reasons of electrode swelling and capacity loss, pointing out that the impact of performance should pay more attention to the core process in the development and application of silicon anode.

2.Problems and Current Situation of Silicon Anode

2.1 Natural Property of the Silicon Anode: the electrical conductivity is low at ~10^-3S /cm, forms Li during cell charge and discharge Si alloy volume swelling is large ~400%.

2.2 Several Failure Phenomena of Silicon Anode: particle fragmentation and pulverization, SEI membrane instability, loss of electrical contact, Li-ions trapped at failure sites, etc.

2.3 Several Common Silicon Anode Electrode Improvement Strategies: silicon nanotechnology, silicon surface coating, doped alloy phase, nuclear shell structure, graphite or carbon coated silicon.

Figure 1. Summary of Silicon Anode problems and improvement strategies

 3. Full-battery Design Process

When silicon is used as a full battery anode material, it is necessary to confirm the material formula and process parameters according to the customer’s requirements for the cell performance. The general process is shown in FIG. 2, and the complete battery is finally assembled and the electrochemical performance is verified while ensuring that the customer needs are met.

Figure 2. Battery design flow chart

4.Two Important Performance Analyses of the in Silico Negative Poles

4.1 Electrode Expands

The thickness swelling of the negative electrode can cause the cell thickness swelling, thus affecting the volume energy density of the cell, which is severely reduced when the swelling ratio of the electrode exceeds 60%. The greater the gram capacity of the negative material of the silicon carbon composite and the greater the swelling thickness of the electrode, the thickness swelling of the battery can be quantified by in situ or in-situ methods.

Figure 3. Relationship between electrode energy density and thickness swelling.

4.2 Silicon Anode Full Battery Capacity Decay

The mechanism of capacity decay is different when the silicon anode is assembled into half and full batteries. For half-batteries, because the use of lithium tablets as a side electrode, the lithium source is sufficient, and the whole battery in charging and discharge, and the lithium content is limited, when the battery is formed in the initial charging SEI, consume part of the lithium-ion, the whole battery is constantly decreasing, and the whole battery potential is increasing, which will lead to the available SOC interval offset of positive and negative poles, which leads to the reduction of usable capacity. Since the assembly structure of the half battery and the whole battery is different, the amount of electrolyte added will be different. And the gap structure in the half battery gives it sufficient electrolyte for recycling, but the full battery space limitation makes its capacity decay acceleration due to the late cycle due to the lack of electrolyte.

Figure 4. Capacity attenuation comparison of half-battery and full battery

5. Summary

This paper summarizes the problems of silicon anode application in high energy lithium-ion battery. In order to improve the volume energy density of the battery, it considers the influence of cell system design, analyzes the causes of electrode swelling and capacity loss, and pays more attention to the influence of cell process on performance in the development and application of silicon anode.

6. IEST Related Test Equipment Recommended：

SWE Series In-situ Swelling Analysis System

6.1 A Variety of Cell in-situ Characterization Methods (stress&swelling thickness): the swelling thickness and swelling force of the cell charging and discharge process are measured at the same time, so as to quantify the changes of cell swelling thickness and swelling force.

6.2 More Refined and Stable Test System: Using a highly stable and reliable automatic adjustment platform, equipped with a high precision thickness measurement sensor and a pressure regulation system, the relative thickness measurement resolution is 0 m, to realize the long cycle monitoring of the long-term charging and discharge process of cells.

6.3 Diversity of Environmental Control and Test Functions: SWE series equipment can adjust the temperature of the charge and discharge environment to help study the swelling behavior of cell cells under high and low temperature; In addition to conventional thickness and pressure test, cell swelling force, compression modulus and compression rate can be tested.

7. Reference

Sujong Chae, Minseong Ko,Kyungho Kim,Kihong Ahn and Jaephil Cho Confronting Issues of the Practical  Implementation of Si Anode  in High-Energy Lithium-Ion Batteries .Joule 1, 47–60, September 6, 2017.