Method for improving volumetric specific energy of lithium ion energy storage battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a method for improving volumetric specific energy of a lithium ion energy storage battery. Aiming at the problems of insufficient thin wall of a shell, redundant thickness of a cell unit layer, lack of interlayer collaborative matching design and the like of the existing lithium ion battery, the invention provides the following technical scheme: step 1, shell preparation: preparing a stainless steel nickel-plated ultrathin shell; 2, preparing a positive pole piece; 3, preparing a negative pole piece: selecting a copper foil as a negative pole base material, and coating the surface of the negative pole base material with a negative pole active material; 4, diaphragm preparation: selecting a PET base material, and coating the surface of the base material with ceramic and an adhesive coating; and step 5, assembling the battery core: loading the prepared roll core into a stainless steel nickel-plated ultrathin shell to prepare the lithium ion energy storage battery. According to the invention, about 5% of internal space is saved, more space is provided for arrangement of components such as the battery cell, the thickness of each unit layer of the battery cell is reduced, and more active substances can be arranged in the limited space.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a method for improving the volumetric energy density of lithium-ion energy storage batteries. Background Technology

[0002] With the rapid iteration of new energy technologies, lithium-ion batteries, with their advantages such as high voltage and long cycle life, have become core energy storage devices in fields such as electric vehicles and large-scale energy storage systems. Currently, the market's performance requirements for lithium-ion batteries continue to upgrade, especially energy density and volume utilization, which directly determine the driving range and installation space adaptability of end products, and are key indicators restricting the promotion and application of high-performance lithium-ion batteries.

[0003] However, existing lithium-ion batteries have significant limitations in structural design and material selection, leading to a bottleneck in energy density improvement and making it difficult to meet the urgent market demand. On the one hand, the thickness of battery casing and cell unit layer materials is redundant, resulting in low internal space utilization. Existing technologies mostly use aluminum casings with a thickness of 0.6–1.2 mm as battery shells, whose wall thickness occupies a large amount of internal space. Moreover, the tensile strength and high-temperature resistance of aluminum casings are limited, further restricting the optimization space for thinner casings. At the same time, the material selection of core cell unit layers such as positive electrode substrate, negative electrode substrate, and separator lacks refined design. The redundant thickness of non-active materials leads to the compression of effective energy storage space inside the battery, restricting the loading of active materials. On the other hand, existing technologies do not specifically optimize the thickness ratio of positive electrode sheets, negative electrode sheets, and separators during the winding or stacking assembly process. Imbalance in the interlayer thickness ratio easily leads to uneven core density and interlayer stress concentration, which not only affects the structural stability of the battery but also increases ion transport resistance. In view of this, this invention proposes a method to improve the volumetric energy density of lithium-ion energy storage batteries. Summary of the Invention

[0004] The purpose of this invention is to address the problems existing in the background technology of lithium-ion batteries, such as insufficient thin-walled casing, redundant cell unit layer thickness, and lack of interlayer cooperative matching design, and to propose a method to improve the volumetric energy density of lithium-ion energy storage batteries.

[0005] The technical solution of the present invention: a method for improving the volumetric energy density of lithium-ion energy storage batteries, comprising the following steps:

[0006] Step 1: Shell preparation: Prepare a stainless steel nickel-plated ultrathin shell, wherein the substrate thickness of the stainless steel nickel-plated shell is 0.25-0.35mm;

[0007] The base material composition by weight percentage is: Cr 16-18%, Ni 8-10%, C 0.02-0.04%, with the balance being Fe;

[0008] A chemically plated nickel layer is prepared on the surface of a substrate. The nickel layer has a thickness of 2-5 μm, a phosphorus content of ≥10%, and a porosity of ≤0.1%.

[0009] Step 2, Preparation of positive electrode sheet: Carbon-coated aluminum foil with a thickness of 10-12μm is selected as the positive electrode substrate, and the surface of the positive electrode substrate is coated with fourth-generation ultra-high pressure lithium iron phosphate as the positive electrode active material.

[0010] Step 3: Preparation of negative electrode sheet: Select copper foil as negative electrode substrate, coat the negative electrode active material on the surface of negative electrode substrate, and control the double-sided surface density of negative electrode sheet to be 163-167 g / m².

[0011] Step 4, membrane preparation: Select PET substrate and coat the substrate surface with a ceramic and adhesive coating with a coating thickness of 1-3 μm;

[0012] Step 5, Cell Assembly: The positive electrode sheet, separator, and negative electrode sheet are stacked or wound in sequence to form a core. The core is then inserted into the stainless steel nickel-plated ultra-thin shell prepared in Step 1. After laser welding, liquid injection, and formation processes, a lithium-ion energy storage battery is obtained.

[0013] Optionally, the stainless steel nickel-plated shell described in step one has a tensile strength of 450-550 MPa, a melting point of 1500-1550℃, and a substrate thickness of 0.25-0.35 mm.

[0014] Optionally, the electroless nickel plating layer mentioned in step one is prepared using an electroless nickel-phosphorus plating process, with the adhesion between the nickel plating layer and the substrate being 50-60 MPa, the thickness of the nickel plating layer being 2-5 μm, and the phosphorus content being 10-12%.

[0015] Optionally, the substrate components in step one, by weight percentage, are: Cr 17%, Ni 9%, C 0.03%, with the balance being Fe.

[0016] Optionally, in step five, the thickness ratio of the positive electrode sheet, the negative electrode sheet, and the separator is controlled to be (5-6):(4-5):1 to ensure the compactness of the core.

[0017] Optionally, the compaction density of the positive electrode sheet is 2.5-2.65 g / cm³;

[0018] The thickness of the PET substrate is 6-8 μm;

[0019] The thickness of the negative electrode substrate is 4-5 μm.

[0020] Optionally, the fourth-generation ultra-high compaction lithium iron phosphate described in step two has a particle size D50 of 2.5-3.5 μm, a compaction density of 2.5-2.65 g / cm³, and a carbon-coated aluminum foil thickness of 10-12 μm.

[0021] The carbon coating thickness of the carbon-coated aluminum foil is 0.5-1μm, and the mass ratio of conductive carbon black to graphite in the carbon coating is 1:2-1:3.

[0022] Optionally, the negative electrode active material mentioned in step three is artificial graphite, the thickness of the negative electrode substrate copper foil is 4-5μm, the tensile strength of the copper foil is 300-350MPa, and the double-sided surface density of the negative electrode sheet is 160-170g / m².

[0023] Optionally, in step four, the ceramic particles are nano-sized alumina with a particle size of 50-100 nm, and the adhesive is polyvinylidene fluoride.

[0024] Optionally, the tension during the winding or stacking process in step five is 0.8-1.2N, and the interlayer gap is 0.05-0.1μm;

[0025] The formation process adopts a constant current and constant voltage mode, with a formation current of 0.02-0.05C, a termination voltage of 3.60-3.65V, and a formation time of 8-12h.

[0026] In summary, this application includes at least one of the following beneficial technical effects:

[0027] This invention employs an ultra-thin stainless steel nickel-plated shell with a thickness of only 0.25-0.35mm. Compared to the traditional aluminum shell with a thickness of 0.6-1.2mm in the prior art, the wall thickness reduces the space occupied by 40%-80%, which can directly save about 5% of the internal space of the battery. This effectively solves the space waste problem caused by insufficient thin-walled design of existing lithium-ion battery shells. At the same time, the tensile strength of this stainless steel nickel-plated shell is improved, and the structural strength and high-temperature resistance are greatly enhanced. While achieving thin-walled design, it ensures the protective reliability of the battery shell and provides a sufficient space basis for the rational arrangement of battery cell components.

[0028] Furthermore, by selecting carbon-coated aluminum foil as the positive electrode substrate, copper foil as the negative electrode substrate, and PET as the ceramic separator, and by controlling the thickness of the carbon-coated aluminum foil, copper foil, and PET substrate, thickness is saved compared to conventional materials; combined with the fourth-generation ultra-high pressure lithium iron phosphate positive electrode active material, the thickness of the unit layer is further reduced, and the thickness of the inactive material is precisely optimized, significantly increasing the loading of active material in a limited space, laying a core foundation for improving battery energy density;

[0029] Furthermore, by addressing the issues of uneven core density and interlayer stress concentration caused by the lack of interlayer collaborative matching design in existing technologies, this collaborative design not only improves the structural stability of the cell but also reduces interlayer ion transport resistance, ensuring the smoothness of the battery charging and discharging process.

[0030] In summary, the casing of this invention saves approximately 5% of the internal space, providing more space for the arrangement of components such as battery cells, which is beneficial to improving the overall performance of the battery, reducing the thickness of each cell layer, and allowing more active materials to be arranged in a limited space, thus laying the foundation for improving the energy density of the battery. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0032] Example 1

[0033] This invention proposes a method for improving the volumetric energy density of lithium-ion energy storage batteries, comprising the following steps:

[0034] Step 1: Shell preparation: Prepare a stainless steel nickel-plated ultrathin shell with a substrate thickness of 0.3 mm. The substrate composition by weight percentage is: Cr 17%, Ni 9%, C 0.03%, with the balance being Fe. Prepare a chemical nickel plating layer on the surface with a thickness of 3 μm, a phosphorus content of 11%, and a porosity of 0.08%. The shell has a tensile strength of 480 MPa and a melting point of 1530 °C.

[0035] Step 2: Preparation of the positive electrode: 11μm carbon-coated aluminum foil with a carbon coating thickness of 0.8μm was selected. The mass ratio of conductive carbon black to graphite was 1:2.5. Fourth-generation ultra-high pressure lithium iron phosphate with a D50 of 3μm was coated, and the compaction density was 2.6g / cm³. 3 .

[0036] Step 3: Preparation of the negative electrode sheet: 4.5μm copper foil with a tensile strength of 320MPa is selected and coated with artificial graphite with a double-sided surface density of 165g / m³. 2 .

[0037] Step 4, membrane preparation: 7μm PET substrate is selected and coated with nano-sized alumina with a particle size of 70nm, and polyvinylidene fluoride coating with a thickness of 2μm.

[0038] Step 5, Cell Assembly: The positive electrode sheet, separator, and negative electrode sheet are wound in a thickness ratio of 5.5:4.5:1 with a winding tension of 1.0N and an interlayer gap of 0.08μm. After the core is installed into the shell, it is laser welded. After liquid injection, it is formed for 10 hours with a current of 0.03C and a termination voltage of 3.63V to obtain the battery.

[0039] Example 2

[0040] This invention proposes a method for improving the volumetric energy density of lithium-ion energy storage batteries, comprising the following steps:

[0041] Step 1: Shell preparation: Prepare a stainless steel nickel-plated ultrathin shell with a substrate thickness of 0.25 mm. The substrate composition by weight percentage is: Cr 16%, Ni 8%, C 0.02%, with the balance being Fe. Prepare a chemical nickel plating layer on the surface with a thickness of 2 μm, a phosphorus content of 10%, and a porosity of 0.05%. The shell has a tensile strength of 450 MPa and a melting point of 1500 °C.

[0042] Step 2: Preparation of the positive electrode: 10μm carbon-coated aluminum foil was selected, with a carbon coating thickness of 0.5μm. The mass ratio of conductive carbon black to graphite was 1:2. Fourth-generation ultra-high pressure lithium iron phosphate with a D50 of 2.5μm and a compaction density of 2.5g / cm³ was then applied. 3 .

[0043] Step 3: Preparation of negative electrode sheet: 4μm copper foil with a tensile strength of 300MPa is selected and coated with artificial graphite with a double-sided surface density of 160g / m³. 2 .

[0044] Step 4, membrane preparation: Select 6μm PET substrate, coat it with nano-sized alumina with a particle size of 50nm and polyvinylidene fluoride coating with a thickness of 1μm.

[0045] Step 5, Cell Assembly: The positive electrode sheet, separator, and negative electrode sheet are wound in a thickness ratio of 5:4:1 with a winding tension of 0.8N and an interlayer gap of 0.05μm. After the core is installed into the shell, it is laser welded. After liquid injection, it is formed for 8 hours with a current of 0.02C and a termination voltage of 3.60V to obtain the battery.

[0046] Example 3

[0047] This invention proposes a method for improving the volumetric energy density of lithium-ion energy storage batteries, comprising the following steps:

[0048] Step 1: Shell preparation: Prepare a stainless steel nickel-plated ultrathin shell with a substrate thickness of 0.35 mm. The substrate composition by weight percentage is: Cr 18%, Ni 10%, C 0.04%, with the balance being Fe. Prepare a chemical nickel plating layer on the surface with a thickness of 5 μm, a phosphorus content of 12%, and a porosity of 0.1%. The shell has a tensile strength of 550 MPa and a melting point of 1550 °C.

[0049] Step 2: Preparation of the positive electrode: 12μm carbon-coated aluminum foil was selected, with a carbon coating thickness of 1μm. The mass ratio of conductive carbon black to graphite was 1:3. Fourth-generation ultra-high pressure lithium iron phosphate with a D50 of 3.5μm and a compaction density of 2.65g / cm³ was then applied. 3 .

[0050] Step 3: Preparation of negative electrode sheet: Select 5μm copper foil with a tensile strength of 350MPa, coat it with artificial graphite, and have a double-sided surface density of 170g / m³. 2 .

[0051] Step 4, membrane preparation: 8μm PET substrate is selected, coated with nano-sized alumina with a particle size of 100nm, and coated with polyvinylidene fluoride with a thickness of 3μm.

[0052] Step 5, Cell Assembly: The positive electrode sheet, separator, and negative electrode sheet are wound in a thickness ratio of 6:5:1 with a winding tension of 1.2N and an interlayer gap of 0.1μm. After the core is installed into the shell, it is laser welded. After liquid injection, it is formed for 12 hours with a current of 0.05C and a termination voltage of 3.65V to obtain the battery.

[0053] Comparative Example

[0054] Shell preparation: 0.9mm aluminum shell with tensile strength of 220MPa and melting point of 600℃.

[0055] Positive electrode preparation: 17μm ordinary aluminum foil was selected and coated with conventional lithium iron phosphate with a compaction density of 2.3g / cm³.

[0056] Negative electrode preparation: 8μm copper foil was selected and coated with artificial graphite, with a double-sided surface density of 165g / m². 2 .

[0057] Separator preparation: 14μm PET substrate and ceramic coating were selected, with a total thickness of 16μm.

[0058] Cell assembly: without thickness ratio control, winding tension 1.5N, interlayer gap 0.2μm; the battery is produced by conventional 0.1C current and 3.7V termination voltage formation for 6 hours.

[0059] Based on the above embodiments and comparative examples, the performance data of the prepared energy storage battery were measured, and the following data table was obtained:

[0060] Table 1 Comparison of Performance Indicators of Lithium-ion Energy Storage Batteries

[0061] Performance indicators Example 1 Example 2 Example 3 Comparative Example Shell wall thickness (mm) 0.3 0.25 0.35 0.9 Total thickness of cell unit layer (μm) 22.5 20 25 39 Compacted density of positive electrode active material (g / cm³) 2.6 2.5 2.65 2.3 Volumetric energy (Wh / L) 370 355 380 330 Cycle life (cycles, 1C charge / discharge, capacity retention ≥80%) 2100 1900 2200 1500 Shell tensile strength (MPa) 480 450 550 220 Interlayer gap (μm) 0.08 0.05 0.1 0.2

[0062] Based on the data table above, we can conclude that:

[0063] Space and material utilization: The embodiment uses a 0.25-0.35mm stainless steel nickel-plated shell, which is only 27.8%-38.9% of the thickness of the aluminum shell in the comparative example. The total thickness of the cell unit layer is reduced by 35.9%-48.7% compared with the comparative example. Combined with a positive electrode active material compaction density of 2.5-2.65g / cm³, compared with only 2.3g / cm³ in the comparative example, the active material loading is significantly improved in a limited space.

[0064] Energy density: The volumetric energy density of the embodiment is 355-380Wh / L, which is 12.1%-15.2% higher than that of the comparative example of 330Wh / L, directly demonstrating the optimization effect of the present invention on battery energy density.

[0065] Structure and Cyclic Performance: The shell tensile strength of the embodiment is 450-550 MPa, which is 2.05-2.5 times that of the comparative example (220 MPa). The interlayer gap is reduced to 0.05-0.1 μm, compared to 0.2 μm in the comparative example. This supports an increase in the cycle life of the embodiment to 1900-2200 cycles, which is 26.7%-46.7% higher than the comparative example's 1500 cycles.

[0066] The above specific embodiments are merely several optional embodiments of the present invention. Based on the technical solutions of the present invention and the relevant teachings of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A method for improving the volumetric energy density of lithium-ion energy storage batteries, characterized in that, Includes the following steps: Step 1: Shell preparation: Prepare a stainless steel nickel-plated ultrathin shell, wherein the substrate thickness of the stainless steel nickel-plated shell is 0.25-0.35mm; The base material composition by weight percentage is: Cr 16-18%, Ni 8-10%, C 0.02-0.04%, with the balance being Fe; A chemically plated nickel layer is prepared on the surface of a substrate. The nickel layer has a thickness of 2-5 μm, a phosphorus content of ≥10%, and a porosity of ≤0.1%. Step 2, Preparation of positive electrode sheet: Carbon-coated aluminum foil with a thickness of 10-12μm is selected as the positive electrode substrate, and ultra-high pressure lithium iron phosphate is used as the positive electrode active material to coat the surface of the positive electrode substrate. Step 3: Preparation of negative electrode sheet: Select copper foil as negative electrode substrate, coat the negative electrode active material on the surface of negative electrode substrate, and control the double-sided surface density of negative electrode sheet to be 163-167 g / m². Step 4, membrane preparation: Select PET substrate and coat the substrate surface with a ceramic and adhesive coating with a coating thickness of 1-3 μm; Step 5, Cell Assembly: The positive electrode sheet, separator, and negative electrode sheet are stacked or wound in sequence to form a core. The core is then inserted into the stainless steel nickel-plated ultra-thin shell prepared in Step 1. After laser welding, liquid injection, and formation processes, a lithium-ion energy storage battery is obtained.

2. The method for improving the volumetric energy density of a lithium-ion energy storage battery according to claim 1, characterized in that, The stainless steel nickel-plated shell mentioned in step one has a tensile strength of 450-550MPa, a melting point of 1500-1550℃, and a substrate thickness of 0.25-0.35mm.

3. The method for improving the volumetric energy density of a lithium-ion energy storage battery according to claim 1, characterized in that, The electroless nickel plating layer mentioned in step one is prepared by electroless nickel-phosphorus plating process. The adhesion between the nickel plating layer and the substrate is 50-60 MPa, the thickness of the nickel plating layer is 2-5 μm, and the phosphorus content is 10-12%.

4. The method for improving the volumetric energy density of a lithium-ion energy storage battery according to claim 1, characterized in that, In step one, the substrate components by weight percentage are: Cr 17%, Ni 9%, C 0.03%, with the balance being Fe.

5. The method for improving the volumetric energy density of a lithium-ion energy storage battery according to claim 1, characterized in that, In step five, the thickness ratio of the positive electrode sheet, the negative electrode sheet, and the separator is controlled to be (5-6):(4-5):1 to ensure the compactness of the core.

6. The method for improving the volumetric energy density of a lithium-ion energy storage battery according to claim 1, characterized in that, The compaction density of the positive electrode sheet is 2.5-2.65 g / cm³. 3 ; The thickness of the PET substrate is 6-8 μm; The thickness of the negative electrode substrate is 4-5 μm.

7. The method for improving the volumetric energy density of a lithium-ion energy storage battery according to claim 1, characterized in that, The fourth-generation ultra-high pressure lithium iron phosphate described in step two has a particle size D50 of 2.5-3.5 μm and a positive electrode compaction density of 2.5-2.65 g / cm³. 3 The thickness of the carbon-coated aluminum foil on the positive electrode substrate is 10-12 μm; The carbon coating thickness of the carbon-coated aluminum foil is 0.5-1μm, and the mass ratio of conductive carbon black to graphite in the carbon coating is 1:2-1:

3.

8. The method for improving the volumetric energy density of a lithium-ion energy storage battery according to claim 1, characterized in that, The negative electrode active material mentioned in step three is artificial graphite, the thickness of the copper foil substrate is 4-5 μm, the tensile strength of the copper foil is 300-350 MPa, and the double-sided areal density of the negative electrode sheet is 160-170 g / m². 2 .

9. A method for improving the volumetric energy density of a lithium-ion energy storage battery according to claim 1, characterized in that, In step four, the ceramic particles are nano-sized alumina with a particle size of 50-100 nm, and the adhesive is polyvinylidene fluoride.

10. A method for improving the volumetric energy density of a lithium-ion energy storage battery according to claim 5, characterized in that, In step five, the tension during winding or stacking is 0.8-1.2N, and the interlayer gap is 0.05-0.1μm. The formation process adopts a constant current and constant voltage mode, with a formation current of 0.02-0.05C, a termination voltage of 3.60-3.65V, and a formation time of 8-12h.