Internal Resistance of Lithium Batteries: What You Need to Know

Lithium batteries have become an essential power source for our daily lives, powering everything from smartphones to electric vehicles (EVs). Lithium battery internal resistance determines battery performance, affecting energy flow, heat generation, and overall lifespan.

This guide will explore its definition, differences between different battery types, influencing factors, performance impacts, and practical measurement and reduction techniques, providing you with valuable knowledge to help you optimize your battery experience.

What is Internal Resistance in Lithium Batteries?

Internal resistance of lithium refers to the resistance within a battery cell that restricts the flow of electric current, directly impacting batteries performance. It consists of two main type ohmic resistance and polarization resistance, each playing a distinct role.

Ohmic Resistance

This is the immediate opposition caused by the contact resistance between electrode materials, electrolytes, and diaphragms. A component of total resistance, it can be as low as 0.05 mΩ in specific pouch cells, but the overall internal resistance of lithium typically ranges from 10-50 mΩ depending on design. It leads to an instant voltage drop when current flows.

Polarization Resistance

This includes charge transfer resistance (occurring over 2-5 seconds due to electrochemical reactions) and diffusion resistance (emerging after 5 seconds from concentration polarization of lithium ions). Together, they affect how efficiently energy is delivered.

Recognizing these components is essential for assessing state of health (SOH) and ensuring safe operation, especially in used battery packs. A clear grasp of ion battery internal resistance helps in designing systems that maintain stable voltage drop under load.

Internal Resistance Across Battery Types

Resistance levels vary significantly among battery types, influencing their suitability for different applications. Here’s a breakdown:

Lithium-Ion Batteries

With resistance of the battery typically ranging from 10-50 mΩ, these offer high efficiency and stable voltage drop under load.

LiFePO4 Batteries

With resistance levels of 2-20 mΩ, they provide stability for energy storage. Very attractive for use in RVs, boat trolling motors and golf carts where reliable long-term power is required.

Lead-Acid Batteries

These have higher resistance measurements, around 100-300 mΩ, leading to more energy loss as heat, which suits them better for backup systems rather than rapid charge-discharge cycles.

Nickel-Metal Hydride (NiMH) Batteries

Featuring resistance of the battery typically between 50-150 mΩ, they perform well in moderate-load devices like cordless tools.

This diversity means lithium batteries often strike the best balance for modern high-performance needs, while others serve specific low-cost or backup roles. Choosing the right type depends on your state of charge and application demands.

Factors Influencing Lithium Batteries Internal Resistance

Several factors shape internal resistance of lithium, and managing them can enhance batteries performance.

• Temperature: Internal resistance increasing dramatically as temperatures drop from 50°C to -25°C (122°F to -13°F, up to sevenfold), reducing discharge efficiency. Maintaining 15°C-30°C (59°F to 86°F) with thermal management (e.g., phase change materials) helps.
• Current and Depth of Discharge (DOD): Higher currents and deep DOD elevate resistance of the battery due to slower lithium ions movement. Keeping DOD shallow extends cycle life.
• Electrode and Electrolyte Materials: High-conductivity materials like NMC or LCO, and optimized electrode particle size, can reduce resistance levels by up to 45%, improving ion flow.
• Diaphragm: Its permeability affects ion battery internal resistance, an optimized design enhances ion movement.
• Collector: Using copper or aluminum collectors lowers contact resistance, aiding electron transfer.
• Manufacturing Quality: Uniform electrode thickness, added tabs, coating techniques, and compaction density during battery cell production reduce internal resistance measurement issues, with quality control like Raman spectroscopy ensuring consistency.
• Aging and Degradation: Over time, internal resistance increasing due to material wear and cycle life impacts state of health (SOH). Proper storage conditions mitigate this.

Impact of Internal Resistance on Lithium Batteries Performance

Internal resistance of lithium significantly affects how lithium ion batteries perform in real-world use. Consider these effects:

• Voltage Output and Sag: High resistance of the battery causes voltage drop during heavy use (e.g., gaming on a smartphone), potentially triggering shutdowns.
• Efficiency and Energy Loss: Increased resistance measurements waste energy as heat, reducing EV range by up to 23.5%.
• Capacity and Runtime: Rising internal resistance increasing lowers usable capacity, shortening EV runtime between charges.
• Heat Generation and Battery Health: Excess heat from high resistance levels can raise operating temperature by 5-10°C (41-50°F), accelerating degradation by up to 20% over 500 cycles, shortening lifespan.

Effective thermal management and cooling systems can prevent these problems and ensure long-term reliable battery performance. If you are looking for a high-performance and stable 12V 36V or 48V lithium battery, Temgo batteries have built-in BMS to actively manage and monitor battery health status. Depending on the use requirements, we also provide lithium batteries with self-heating function.

How to Measure Internal Resistance

Accurately measuring internal resistance of lithium is vital for maintaining battery cell health. Here are proven methods:

• Voltage Drop Method: Measure open-circuit voltage, apply a load, and use Ohm’s Law (R = V/I) to calculate resistance of the battery.
• AC Impedance Spectroscopy: Analyze impedance across a range of frequencies (e.g., 0.1 Hz to 10 kHz) to assess ohmic resistance, charge transfer resistance, and diffusion resistance.
• DC Internal Resistance Method: Apply a short pulse and measure the voltage drop (U/I) for a quick internal resistance measurement.
• Pulse Discharge Method: Use a high-current pulse to measure voltage drop, ideal for rapid assessments.
• Hybrid Pulse Power Characterization (HPPC): Combines DC and AC techniques for a comprehensive measurement method.

For industrial use, tools like electronic testers and load testers provide accurately measure results. Always stay within safe current limits to avoid damaging the battery cell.

Strategies to Reduce Lithium Batteries Internal Resistance

Reducing internal resistance of lithium enhances lithium ion battery efficiency and lifespan. The following steps help professionals maximize battery performance, implement these strategies:

• Optimize Charging: Use constant current charging to minimize heat, avoiding fast charging unless necessary.
• Material Selection: Choose high-grade electrodes (e.g., NMC, LCO) and electrolytes to lower resistance levels.
• Thermal Management: Maintain optimal temperatures with phase change materials or liquid cooling to reduce internal resistance increasing.
• Manufacturing Improvements: Ensure uniform thickness, add tabs, use coating techniques, and apply Raman spectroscopy for quality control.
• Regular Maintenance: Conduct regular internal resistance measurement, avoid deep discharge, use smart chargers, and avoid required high current rates to preserve battery cell integrity. Predictive maintenance (PHM) systems can further enhance state of health (SOH).