Date: 2026-01-12 hits: 110
The direct current internal resistance (DCIR) of a lithium-ion battery is one of the key indicators of its performance, directly affecting its charging and discharging efficiency, power output, and lifespan. The accuracy and stability of DCIR test results are crucial for evaluating the quality and performance of lithium-ion batteries. The core processes affecting lithium-ion battery DCIR testing are concentrated in three main stages: electrode preparation, cell assembly, and formation and aging. The following will provide a detailed analysis of the specific key processes in each stage.
I. Electrode Preparation Process
(I) Electrode Coating
During the electrode coating process, the coating quality significantly affects DCIR. Uneven coating is a common problem; if the active material is locally too thick or too thin, it will lead to uneven current distribution. When the current is unevenly distributed on the electrode, it will increase local resistance, thus directly increasing the DCIR. In addition, insufficient coating material can cause local areas without active material, forming "virtual contacts." This "virtual contact" is like a break in the circuit, causing significant resistance to current flow, significantly increasing internal resistance, and thus affecting the DCIR test results.
(II) Electrode Rolling
The degree of electrode rolling also has a significant impact on DCIR. If the rolling is too loose, the electrode porosity is too high, and the active material is not in close contact with the current collector. This hinders the transmission of electrons between the active material and the current collector, resulting in higher internal resistance and increased DCIR. Conversely, if the rolling is too tight, it can damage the active material structure and block ion channels. When ion channels are blocked, ion transport becomes difficult, which also increases DCIR.
(III) Electrode Cutting/Slitting
During the electrode cutting/slitting process, if burrs generated during cutting are not removed, a series of problems can arise. Burrs may puncture the separator, leading to micro-short circuits. Micro-short circuits can cause abnormal current paths inside the battery, increasing resistance and resulting in abnormally high DCIR test results. In addition, burrs may also lead to poor contact between the electrode and the tab, further affecting current transmission and similarly resulting in abnormally high DCIR.
II. Battery Cell Assembly Process
(I) Tab Welding
The quality of tab welding is a crucial factor affecting DCIR. Poor welding, such as incomplete or faulty welds, can significantly increase the contact resistance between the tab and the current collector. Incomplete or faulty welds result in a weak connection between the tab and the current collector, leading to high contact resistance when current flows, thus causing the DCIR to exceed the limit. Additionally, residual welding slag can cause poor contact, which is another common reason for excessive DCIR. The presence of welding slag hinders the normal transmission of current, increasing resistance and affecting the DCIR test results.
(II) Cell Winding/Stacking
Process control during cell winding/stacking significantly impacts DCIR. Winding misalignment, such as electrode sheet offset or stacking misalignment, reduces the effective contact area between the positive and negative electrodes. Reduced effective contact area increases ion transport resistance, making it difficult for ions to move within the battery, thus leading to an increase in DCIR. Furthermore, uneven winding tension can cause separator wrinkles, which affect ion conduction, further increasing resistance and impacting the DCIR test results.
(III) Electrolyte Filling Process
The electrolyte filling process primarily affects DCIR through the amount of electrolyte and the standing time after filling. Insufficient electrolyte volume prevents the electrolyte from fully wetting the electrodes, creating "dry areas." The presence of "dry areas" prevents normal ion transport in these regions, increasing internal resistance and leading to a higher DCIR. Insufficient standing time after electrolyte filling also results in inadequate wetting of the electrodes, affecting ion transport and causing a higher DCIR.
III. Formation and Aging Process
(I) Formation Process
The formation process parameters have a significant impact on the formation of the SEI film, which in turn affects the DCIR. Insufficient formation current or short formation time can lead to incomplete and non-dense SEI (solid electrolyte interface) film formation. An incomplete and non-dense SEI film cannot effectively protect the electrode material during subsequent battery cycling, causing the internal resistance to continuously increase. In addition, abnormal formation temperature also affects the quality of the SEI film. Different temperature conditions affect the composition and structure of the SEI film, indirectly changing the DCIR.
(II) Aging Process
The impact of the aging process on DCIR is mainly reflected in the aging time and aging environment temperature. Insufficient aging time means that the electrolyte and electrode sheets have not fully reacted, and the SEI film is not stable. An unstable SEI film affects ion transport and battery performance, leading to higher DCIR test results. Excessive fluctuations in the aging environment temperature can lead to poor consistency in the DCIR of different cells. Under fluctuating temperatures, the internal chemical reactions and ion transport in different cells will vary, resulting in differences in DCIR test results.
IV. Conclusion
In summary, the core processes affecting lithium battery DCIR testing are concentrated in three major stages: electrode preparation, cell assembly, and formation and aging. The coating, rolling, and cutting/slitting processes in electrode preparation; the tab welding, winding/stacking, and electrolyte injection processes in cell assembly; and the formation and aging processes in the formation and aging stage—each step's process control has a significant impact on DCIR. In the production of lithium batteries, it is necessary to strictly control the process parameters of these key processes to ensure that the DCIR test results of lithium batteries meet the requirements and improve the quality and performance of lithium batteries. At the same time, for abnormal DCIR situations, it is necessary to start from these core processes, conduct a comprehensive investigation and analysis, identify the problem, and solve it promptly.
