How Carrar Inhibits LFP Battery Degradation

Foreword

Much has been written about the advantages of lithium-ion phosphate (LFP) batteries, including their use of abundant, non-toxic materials that are less damaging to extract.

LFPs also offer a broader operational temperature range and higher heat tolerance than their NMC (nickel manganese cobalt) counterparts, reducing the risk of thermal runaway and potentially enabling longer lifespans.

LFP batteries, however, are still batteries. As such, they degrade over time.  Energy availability and power output decrease. This process is influenced by high C-rates, but more so by high temperatures.

Interestingly, the mechanism that makes LFP batteries more heat-resistant in the short term can accelerate battery aging in the long run.

(It should be noted that we lack independent validation of LFP’s thermal stability, and that BYD’s Atto 3 battery warranty, for example, is 8 years/150,000 km – in line with warranties of most NMC-equipped vehicles.)

The Key Drivers of LFP Battery Aging

Battery degradation in LFP cells is caused by three interconnected physicochemical, thermal, and mechanical processes that evolve over time:

• Loss of Active Material (LAM) due to mechanical and chemical degradation of electrode structure and components.
• Loss of Lithium Inventory (LLI), primarily from the formation and breakdown of the solid electrolyte interphase (SEI) layer.
• Increased Internal Resistance, stemming from slowed electrochemical kinetics.

The SEI layer’s continual formation and eventual disintegration are the most critical contributors among these. This layer, which forms on the carbon anode through the reduction of the organic electrolyte, is a double-edged sword; initially, it protects the electrode by preventing further electrolyte decomposition. Over time, however, it “traps” (immobilizes) the lithium ions.

This “trapping”, caused by lithium ions intercalating between anode layers, reduces the ion availability for cycling. This leads to uneven electrical flow and temperature distribution, increased resistance, creation of hotspots, and ultimately a shortened battery life.

Why Temperature Matters

Numerous studies have demonstrated that LFP battery degradation accelerates at higher temperatures, particularly at high C-rates. Stronger currents cause greater ohmic heating, which further raises internal temperatures and intensifies degradation.

In the chart below (taken from often-cited LFP tests), the light gray line represents battery capacity reduction (as a function of cycles) at 30°C, while the dark gray line represents the same battery at 45°C.

At 30°C, the battery reaches its end-of-life threshold (80% capacity) after over 3,000 cycles. At 45°C, it reaches this point in under 1,000 cycles.

How Carrar’s Thermal Management System Inhibits Degradation

Simply put, Carrar maintains the battery cells at a stable 25°C using a two-phase cooling system that wraps the battery cell 360°.

This tight thermal control delivers two major benefits:

1. Slower SEI Layer and Electrolyte Degradation. Maintaining an optimal, consistent temperature significantly slows SEI formation and decomposition, thereby preserving lithium inventory and reducing resistance buildup.
2. Delay of the Knee Point Events. With standard thermal management systems, LFP battery degradation isn’t smooth, but progresses in sudden capacity drops known as Knee Points. As seen in the graph below, Carrar delays the Knee Points to the end of the battery life.

Carrar’s battery thermal management system ensures uniform temperature across the cell, significantly slowing the degradation processes (such as lithium plating, electrode saturation, and electrolyte depletion), as well as ion-flow irregularities and Knee-Point events.

Delaying the Knee Point to the end of life also has major benefits for battery longevity. As can be seen below, the battery remains above the 80% capacity threshold for much longer (over 6,000 cycles) in this test, before hitting the Knee Point. The battery also ages more predictably, enhancing usable life and safety.

FEC – Full Equivalent cycles.