Battery Pack with Iron-Phosphorus Cathode for Thermal Stability
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Solution Overview
Problem
Lithium ion batteries face challenges in high-temperature durability, low-temperature performance, and cycle life due to materials' limitations, particularly with lithium iron phosphate, which requires cooling systems, increasing weight and cost, and struggles with high interfacial resistance and metal deposition issues.
Innovation Solution
A battery pack with nonaqueous electrolyte batteries connected in series, featuring a positive electrode with an iron-containing phosphorus compound and a titanium-containing oxide, controlled charge maximum voltage between 4 V to 5 V, and a negative electrode with a titanium-containing oxide, enhancing durability and cycle life without forced cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium iron phosphate is used as positive electrode active material to improve thermal stability in high-temperature environment, then thermal stability is improved, but electrical conductivity is low resulting in insufficient high output performance
Solution Approach 1:
The patent changes the chemical composition parameters of the positive electrode active material by introducing Mn substitution (Li1-x-yMnxYiPO4 where 0<x<1, 0<y<1-x) and surface coating with elements A, B, or C. This modifies the electrical conductivity and electrochemical performance while maintaining the olivine structure's thermal stability, thereby resolving the contradiction between thermal stability and output performance.
Solution Approach 2:
The patent creates a composite structure by coating the Li1-x-yMnxYiPO4 core with surface-modified layers containing elements A, B, or C. This composite approach combines the high thermal stability of the olivine structure with the enhanced electrical conductivity provided by the surface coating, simultaneously achieving both thermal stability and high output performance.
2Reliability
If iron component is dissolved from lithium iron phosphate at high temperature, then cycle life deterioration is accelerated, but using cooling systems increases volume and weight
Solution Approach 1:
The patent modifies the chemical composition by Mn substitution and surface coating to enhance the structural stability of the positive electrode material at high temperatures. This prevents iron dissolution and maintains cycle life without requiring external cooling systems, thus avoiding the weight penalty of cooling equipment.
Solution Approach 2:
Instead of using cooling systems to manage the harmful effect of high-temperature iron dissolution, the patent converts the problem by chemically stabilizing the material composition itself. The Mn substitution and surface coating transform the inherently unstable LiFePO4 into a thermally stable composite that resists degradation, eliminating the need for active cooling.
3Reliability
If nonaqueous electrolyte is used to improve safety performance, then nonflammability is improved, but output characteristics and low-temperature performance deteriorate
Solution Approach 1:
The patent modifies the electrolyte composition by adding specific additives (0.01-5 wt% of compounds containing F, Cl, or Br atoms) to the nonaqueous electrolyte. This chemical parameter change enhances the electrolyte's conductivity and low-temperature fluidity while maintaining its nonflammable safety characteristics, thereby improving output performance without compromising safety.
Solution Approach 2:
The patent creates a composite electrolyte system by combining the base nonaqueous electrolyte (providing safety) with functional additives (providing enhanced conductivity and low-temperature performance). This composite electrolyte formulation simultaneously achieves nonflammability, high output characteristics, and improved low-temperature operation.
4Power
If thin electrode is formed to increase output, then output is improved, but current collector strength becomes insufficient reducing battery capacity and reliability
Solution Approach 1:
The patent optimizes the electrode thickness and active material particle size parameters to achieve high output without compromising structural integrity. By controlling the electrode to have thickness of 1-50 μm and using ultrafine particles (0.1-10 μm), the design maintains sufficient current collector strength while maximizing output performance.
Solution Approach 2:
The patent applies different properties to different parts of the electrode structure. The current collector is designed with localized reinforcement at critical areas, and the active material is distributed with optimized local density and particle size distribution. This local quality approach allows thin electrode regions to maintain sufficient strength while achieving high overall output.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution improves high-temperature durability and cycle life while maintaining discharge capacity, reducing the battery pack's volume and weight, and allows for integration in vehicles without the need for cooling systems, enhancing performance and efficiency.
Implementation Method 1
a nonaqueous electrolyte
Implementation Method 2
a positive electrode, a negative electrode, and a nonaqueous electrolyte
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
According to one embodiment, a battery module (100) including two nonaqueous electrolyte batteries electrically (101), (102) connected in series is provided. Each of the nonaqueous electrolyte batteries (101), (102) includes a positive electrode (3), a negative electrode (4), and a nonaqueous electrolyte. The positive electrode (3) contains an iron-containing phosphorus compound represented by LixFe1-yMnyAzPO4 and having an olivine structure, wherein A is at least one element selected from the group consisting of V, Mg, Ni, Al, Sn, Zr, and Nb, and 0 ≤ x ≤ 1.1, 0 ≤ y ≤ 0.2, and 0 ≤ z ≤ 0.2 are set. The negative electrode (4) contains a titanium-containing oxide. The battery module (100) has a charge maximum voltage in a range of 4 V to 5 V.