High strength composite current collector with gradient cte and method of making

Abstract

The application belongs to the technical field of composite current collectors, and particularly relates to a high-strength composite current collector with gradient CTE and a preparation method thereof, which comprises a PP base material, the two sides of the base material are symmetrically provided with bonding layers, gradient layers, buffer layers and functional layers in sequence, the material of the gradient layer is composed of the materials of the bonding layers and the functional layers, the gradient layer is provided with at least a first gradient layer, a second gradient layer and a third gradient layer in sequence from the bonding layer to the functional layer, the content of the bonding layer component in each layer is gradually reduced from not less than 70% to not higher than 30%, and the content of the functional layer component is gradually increased from not higher than 30% to not less than 70%, and the CTE thermal stress of the bonding layers, the gradient layers, the buffer layers and the functional layers as a whole is gradiently increased.

Description

Technical Field

[0001] This invention belongs to the field of composite current collector technology, specifically relating to a high-strength composite current collector with gradient CTE and its preparation method. Background Technology

[0002] Lithium-ion batteries are the core of modern electronic devices, and current collectors play a crucial role in them. The main function of a current collector is to carry the positive and negative electrode materials and efficiently collect and transport electrons to ensure the battery's efficient operation. However, traditional current collectors have many drawbacks, which not only affect battery performance but also pose a threat to safety.

[0003] Composite current collectors employ a multi-layered structure design, combining the advantages of different materials to maintain good conductivity while reducing manufacturing costs. This makes them a highly promising new material for lithium-ion batteries. However, despite the many advantages exhibited by composite current collectors, their development is still limited by some key factors.

[0004] One major limitation is that traditional solutions often employ the conventional Ti / Cu coating process, using metallic Ti as the base layer, which results in an interfacial bonding energy of only 0.8 J / m between Ti and the PP substrate. 2 The presence of van der Waals forces leads to unreliable physical adsorption and a CTE (thermal stress) mismatch rate of up to 95%, resulting in thermal stress concentration that easily causes cracking and delamination. This defect makes it difficult to meet the lifespan requirements of power batteries during production and use, and also reduces the finished product qualification rate of the batteries.

[0005] Therefore, overcoming the defect of easy delamination in Ti / Cu composite current collectors is a technical problem that urgently needs to be solved in this field.

[0006] It should be noted that the information disclosed in this background section is only for understanding the background technology of this application concept, and therefore, the above description is not considered to constitute prior art information. Summary of the Invention

[0007] This disclosure provides at least one high-strength composite current collector with gradient CTE and its preparation method.

[0008] In a first aspect, embodiments of this disclosure provide a high-strength composite current collector with gradient CTE, comprising: a PP substrate, on which an adhesive layer, a gradient layer, a buffer layer, and a functional layer are symmetrically disposed in sequence on both sides; the material of the gradient layer is composed of a mixture of the materials of the adhesive layer and the functional layer; the gradient layer is provided with at least a first gradient layer, a second gradient layer, and a third gradient layer in sequence from the adhesive layer to the functional layer, and the content of the adhesive layer component in each layer decreases from not less than 70% to not more than 30% in each layer, and the content of the functional layer component increases from not more than 30% to not less than 70% in each layer; and the CTE thermal stress of the adhesive layer, gradient layer, buffer layer, and functional layer increases in a gradient overall.

[0009] In one optional embodiment, the surface of the PP substrate is activated by plasma pretreatment and then sputtered with an adhesive layer, and the thickness of the PP substrate ranges from 2 to 50 μm.

[0010] In one optional embodiment, the adhesive layer is made of Ti and has a thickness ranging from 5 to 10 nm.

[0011] In one optional embodiment, the total thickness of the gradient layer ranges from 20 to 50 nm; and the thickness of a single gradient layer is not less than 5 nm.

[0012] In one optional embodiment, the buffer layer is made of Ni and has a thickness ranging from 20 to 50 nm.

[0013] In one optional embodiment, the material of the functional layer is Cu, and the thickness of the functional layer ranges from 200 to 1500 nm.

[0014] In one optional implementation, the CTE range of the gradient layer is 9 ppm / ℃ to 15 ppm / ℃.

[0015] In one optional embodiment, the content of the adhesive layer component in the first gradient layer ranges from 70% to 99%, and the content of the functional layer component ranges from 1% to 30%; the content of the adhesive layer component in the second gradient layer ranges from 40% to 60%, and the content of the functional layer component ranges from 40% to 60%; the content of the adhesive layer component in the third gradient layer ranges from 1% to 30%, and the content of the functional layer component ranges from 70% to 99%.

[0016] Secondly, this disclosure also provides a method for preparing a high-strength composite current collector with gradient CTE as described above, comprising the following steps: plasma activation of a PP substrate to obtain a pretreated PP substrate; sputtering on both sides of the pretreated PP substrate to prepare an adhesive layer; segmented co-sputtering of dual targets on the outer side of the adhesive layer to prepare a gradient layer; sputtering on the outer side of the gradient layer to prepare a buffer layer; and sputtering on the outer side of the buffer layer to prepare a functional layer.

[0017] Thirdly, embodiments of this disclosure also provide a lithium-ion battery, including a casing, a core, and an electrolyte, wherein the core is formed by winding a positive electrode sheet, a separator, and a negative electrode sheet, wherein the positive electrode sheet and the negative electrode sheet employ a high-strength composite current collector with gradient CTE as described above.

[0018] The beneficial effects of this invention are that the high-strength composite current collector with gradient CTE and its preparation method achieve gradient matching of CTE thermal stress between Ti and Cu by setting a gradient layer, reducing lattice mismatch. During the charging and discharging process of lithium battery, the gradient layer can also absorb strain energy through dislocation slip, further improving the bonding strength of the composite current collector. At the same time, the transition layer can pin the grain boundaries of the functional layer, which not only ensures the change of CTE thermal stress gradient, but also inhibits the grain coarsening of the functional layer at high temperature, avoids the deterioration of conductivity, and forms a high-modulus composite layer to improve the overall scratch resistance and wear resistance of the composite current collector.

[0019] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description and the drawings.

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a high-strength composite current collector with gradient CTE provided in an embodiment of the present disclosure;

[0023] Figure 2This is a schematic diagram of a high-strength composite current collector with gradient CTE provided in an embodiment of the present disclosure;

[0024] Figure 3 SEM image of Embodiment 1 provided in this disclosure;

[0025] Figure 4 SEM image of Comparative Example 4 provided in the embodiments of this disclosure;

[0026] Figure 5 SEM image of Comparative Example 7 provided for embodiments of this disclosure.

[0027] In the picture:

[0028] 1. PP substrate; 2. Adhesive layer; 31. First gradient layer; 32. Second gradient layer; 33. Third gradient layer; 34. Fourth gradient layer; 35. Fifth gradient layer; 4. Buffer layer; 5. Functional layer. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] As used herein, the phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” etc., generally refer to the fact that a particular feature, structure, or characteristic following the phrase can be included in at least one embodiment of this disclosure. Therefore, a particular feature, structure, or characteristic can be included in more than one embodiment of this disclosure, such that these phrases do not necessarily refer to the same embodiment. As used herein, the terms “example,” “exemplary,” etc., are used to “serve as an example, instance, or illustration.” Any implementation, aspect, or design described herein as “example” or “exemplary” is not necessarily to be construed as preferred or superior to other implementations, aspects, or designs. Rather, the use of the terms “example,” “exemplary,” etc., is intended to present concepts in a specific manner.

[0031] In this document, exemplary embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. As used herein, expressions such as “at least one of…” modify the entire list of elements when following a list of elements, rather than individual elements in the list. For example, the expression “at least one of a, b, and c” should be understood to include only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b, and c.

[0032] The terminology used herein is for the purpose of describing specific exemplary configurations only and is not intended to be limiting. As used herein, the singular articles “a,” “an,” and “the” may also be intended to include plural forms unless otherwise clearly stated herein. The terms “comprising,” “including,” and “having” are inclusive and thus specify the presence of features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein should not be construed as requiring them to be performed in the specific order discussed or shown, unless specifically identified as such. Additional or alternative steps may be employed.

[0033] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0034] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0035] Please see Figure 1 ,like Figure 1 As shown, this disclosure provides a high-strength composite current collector with gradient CTE, comprising: a PP substrate, on which an adhesive layer, a gradient layer, a buffer layer, and a functional layer are symmetrically disposed on both sides; the gradient layer is composed of a mixture of the adhesive layer and the functional layer; the gradient layer comprises at least a first gradient layer, a second gradient layer, and a third gradient layer in sequence from the adhesive layer to the functional layer, wherein the content of the adhesive layer component in each layer decreases from not less than 70% to not more than 30%, and the content of the functional layer component increases from not more than 30% to not less than 70%; and the CTE thermal stress of the adhesive layer, gradient layer, buffer layer, and functional layer increases in a gradient overall.

[0036] Specifically, an overall gradient increase means that there is an overall upward trend between each layer. Even if the CTE thermal stress decreases by less than 1 ppm / ℃ between some layers, it can still be regarded as an overall gradient increase.

[0037] In some embodiments, specifically, the surface of the PP substrate is activated by plasma pretreatment and then a sputtered adhesive layer is applied, and the thickness of the PP substrate ranges from 2 to 50 μm.

[0038] Specifically, the dissociation energy of the CH bond in the PP film is as high as 413 kJ / mol. By etching the surface of the PP film with O2 plasma, the C=O functional group is activated and formed. At the same time, Ti atoms hybridize with the p orbitals of the C=O functional group through d orbitals, forming a Ti-OC structure with a bond energy of 318 kJ / mol, which enhances the bonding force between the PP substrate and the metal. In addition, the network formed between covalent bonds also increases the crack propagation work from 0.5 J / m² to 3.2 J / m², further strengthening the bonding force between the PP substrate and the metal.

[0039] In some embodiments, the adhesive layer is made of Ti and has a thickness ranging from 5 to 10 nm.

[0040] In some embodiments, the total thickness of the gradient layer is in the range of 20 to 50 nm; and the thickness of a single gradient layer is not less than 5 nm.

[0041] In some embodiments, the material of the buffer layer is Ni, and the thickness of the buffer layer ranges from 20 to 50 nm.

[0042] Specifically, the CTE thermal stress of the bonding layer Ti is 8.6 ppm / ℃, which is increased through the Ti-Cu gradient layer. The Ni layer with a CTE thermal stress of 13 ppm / ℃ serves as a connection, and finally the Cu layer with a CTE thermal stress of 17 ppm / ℃ achieves a complete thermal stress gradient distribution.

[0043] Specifically, the CTE thermal stress of Cr is 6.2 ppm / ℃, which is lower than that of Ti. Therefore, Ti can shorten the thermal stress gradient distribution range when used as a binder layer. In addition, the CTE difference between Cu and Ni is too small, so using Cu-Ni as a gradient layer will result in an inability to effectively mitigate the stress gradient.

[0044] Specifically, the gradient layer is set in a cycle of -40 to 150°C. The gradient layer can further absorb strain energy through dislocation slip, thereby improving the bond strength.

[0045] In some embodiments, the material of the functional layer is Cu, and the thickness of the functional layer ranges from 200 to 1500 nm.

[0046] Specifically, the lattice mismatch between Ti and Cu is approximately 12%, while that between Ni and Cu is approximately 2.7%. Therefore, setting a transition layer between the gradient layer and the functional layer can further reduce the impact of lattice mismatch. At the same time, the Ni layer can pin the Cu grain boundaries, suppressing grain coarsening at high temperatures (grain size stabilizes at 50-80 nm) and preventing conductivity degradation. Ti (hardness ≈ 800 HV) and Ni (hardness ≈ 600 HV) form a high-modulus composite layer, improving the overall scratch resistance and wear resistance of the current collector.

[0047] In some embodiments, specifically, the CTE range of the gradient layer is 9ppm / ℃ to 15ppm / ℃.

[0048] In some embodiments, specifically, the content of the adhesive layer component in the first gradient layer ranges from 70% to 99%, and the content of the functional layer component ranges from 1% to 30%; the content of the adhesive layer component in the second gradient layer ranges from 40% to 60%, and the content of the functional layer component ranges from 40% to 60%; the content of the adhesive layer component in the third gradient layer ranges from 1% to 30%, and the content of the functional layer component ranges from 70% to 99%.

[0049] Specifically, in structures with more than three layers on one side, the content of the adhesive layer component in the layer closest to the adhesive layer ranges from 70% to 99%, and the content of the functional layer component ranges from 1% to 30%; the content of the adhesive layer component in the middle layer ranges from 40% to 60%, and the content of the functional layer component ranges from 40% to 60%; and the content of the adhesive layer component in the layer closest to the transition layer ranges from 1% to 30%, and the content of the functional layer component ranges from 70% to 99%.

[0050] This disclosure also provides a method for preparing a high-strength composite current collector with gradient CTE as described above, comprising the following steps: plasma activation of a PP substrate to obtain a pretreated PP substrate; sputtering on both sides of the pretreated PP substrate to prepare an adhesive layer; segmented co-sputtering of dual targets on the outside of the adhesive layer to prepare a gradient layer; sputtering on the outside of the gradient layer to prepare a buffer layer; and sputtering on the outside of the buffer layer to prepare a functional layer.

[0051] This disclosure also provides a lithium-ion battery, including a casing, a core, and an electrolyte, wherein the core is formed by winding a positive electrode sheet, a separator, and a negative electrode sheet, wherein the positive electrode sheet and the negative electrode sheet employ a high-strength composite current collector with gradient CTE as described above.

[0052] Preparation process:

[0053] Materials and Equipment

[0054] equipment:

[0055] Roll-up magnetron sputtering system (equipped with Ti target, Cu target, Ni target, and plasma cleaning module);

[0056] Plasma generator (RF power supply, 13.56MHz).

[0057] Material:

[0058] PP film (thickness 2-50um, initial surface energy 30mN / m);

[0059] Ti target (purity > 99.99%), Cu target (purity > 99.99%), Ni target (purity > 99.95%);

[0060] Ar gas (99.999%), O2 gas (99.999%).

[0061] Process steps:

[0062] S1, PP substrate pretreatment, the parameters set include: O2 / Ar mixed gas (O2 ratio 20%, total flow rate 50sccm), power RF 500W, gas pressure 0.1Pa;

[0063] S2, adhesive layer sputtering, the set parameters include: Ti target (DC power supply), power of 1500~3000W, Ar flow rate of 30sccm, gas pressure of 0.5Pa, winding speed of 1m / min, winding time of 1min, and deposition thickness of 5nm.

[0064] S3, gradient layer sputtering, with parameters set as follows: initial power of Ti target is 500W, linear stiffness is 0W, initial power of Cu target is 0W, linearly increasing to 500W;

[0065] The winding speed was 1 m / min, the Ar flow rate was 30 sccm, and the air pressure was 0.3 Pa.

[0066] S4, buffer layer sputtering, the set parameters include: Ni target (DC power supply), power of 1500~3000W, Ar flow rate of 30sccm, gas pressure of 0.5Pa, winding speed of 1m / min, winding time of 1min, and deposition thickness of 20nm.

[0067] S5, functional layer sputtering, with the following parameters: Cu target (DC power supply), power of 5000W, Ar flow rate of 50sccm, gas pressure of 0.2Pa, winding speed of 1m / min, winding time of 1min, and deposition thickness of 1000nm.

[0068] Specifically, in step S1, the pretreatment generates polar groups on the PP surface, increases the surface energy to no less than 50 mN / m, and reduces the contact angle from 110° to 30°.

[0069] For details, please refer to Figure 2 ,like Figure 2 As shown, the high-strength composite current collector with gradient CTE of Example 1 was obtained according to the above process. By changing some parameters, Examples 1-5 shown in Table 1, Comparative Examples 1-3 shown in Table 2, Comparative Examples 4-5 shown in Table 3, Comparative Examples 6-7 shown in Table 4 and Comparative Example 8 shown in Table 5 were obtained.

[0070] Table 1

[0071]

[0072]

[0073] Table 2

[0074]

[0075] Table 3

[0076]

[0077] Table 4

[0078]

[0079] Table 5

[0080]

[0081] Please see Figure 3 ,like Figure 3 As shown, the SEM image of the high-strength composite current collector with gradient CTE obtained in Example 1 after high-temperature aging shows that the particle size is dense, without defects or pores, and without agglomeration.

[0082] Specifically, in Example 2, the gradient layer thickness is reduced, resulting in a less gentle stress distribution than in Example 1, which is reflected in a decrease in the bonding strength during tape testing.

[0083] Specifically, in Example 3, only a single layer with a Cu / Ti ratio of 5:5 was set, which increased the stress at the stepped interface and led to an increase in interface defects.

[0084] Specifically, in Example 5, the increased thickness of the transition layer Ni leads to accelerated grain boundary diffusion, which in turn increases the electrical resistance.

[0085] Specifically, in Comparative Example 1, no gradient layer was set, and the adhesive layer and transition layer were directly connected. This caused thermal stress concentration, deterioration under high temperature environment, and delamination.

[0086] Specifically, in Comparative Example 3, without a buffer transition layer, grain boundary diffusion is accelerated. This is partly because the absence of a transition layer to pin the grain boundaries of the functional layer leads to a decrease in interlayer bonding strength, and partly because the inability to form a high-modulus composite layer significantly reduces the critical scratch load of the composite current collector.

[0087] Please see Figure 4 ,like Figure 4As shown, the SEM image of the composite current collector obtained in Comparative Example 5 after high-temperature aging shows that strip-shaped agglomerates and pores appear on the film surface. Compared with Example 1, Comparative Example 5 changed Ti in the adhesive layer and gradient layer to Ni. Since the difference in CTE between Cu and Ni is too small, and the metal Ni and NiCu alloy layer deteriorate and agglomerate faster after high-temperature aging, Cu-Ni as a gradient layer cannot better relieve stress gradient. Therefore, the interlayer bonding effect and high-temperature resistance are significantly worse than those of Example 1.

[0088] Please see Figure 5 ,like Figure 5 As shown, the SEM image of the composite current collector obtained in Comparative Example 7 after high-temperature aging shows dense agglomeration and large pores on the film surface. That is, the current collector with only a copper functional layer will show obvious high-temperature agglomeration. However, this phenomenon will be weakened after adding other materials, and the Cu / Ti gradient layer is the preferred solution.

[0089] Specifically, in Comparative Example 8, the gradient layer reverse design resulted in poor lattice matching, increased resistance, and a significant decrease in adhesion.

[0090] In summary, this high-strength composite current collector with gradient CTE and its preparation method achieve gradient matching of CTE thermal stress between Ti and Cu by setting a gradient layer, reducing lattice mismatch. During the charging and discharging process of lithium battery, the gradient layer can also absorb strain energy through dislocation slip, further improving the bonding strength of the composite current collector. At the same time, the transition layer can pin the grain boundaries of the functional layer, which not only ensures the change of CTE thermal stress gradient, but also inhibits the grain coarsening of the functional layer at high temperature, avoids the degradation of conductivity, and forms a high-modulus composite layer to improve the overall scratch resistance and wear resistance of the composite current collector.

[0091] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A high strength composite current collector with a gradient CTE, characterized in that, It comprises: a PP substrate, whose two sides are symmetrically provided with, in sequence, an adhesive layer, a gradient layer, a buffer layer and a functional layer; the material of the gradient layer is composed of the materials of the adhesive layer and the functional layer; the gradient layer is provided with, in sequence from the adhesive layer to the functional layer, at least a first gradient layer, a second gradient layer and a third gradient layer, and the content of the adhesive layer component in each layer decreases from not less than 70% to not higher than 30%, and the content of the functional layer component increases from not higher than 30% to not less than 70%; the CTE thermal stress of the adhesive layer, the gradient layer, the buffer layer and the functional layer as a whole presents a gradient increase; the material of the adhesive layer is Ti; the material of the buffer layer is Ni; the material of the functional layer is Cu; the CTE interval range of the gradient layer is 9 ppm / ℃-15 ppm / ℃.

2. The high-strength composite current collector with gradient CTE according to claim 1, wherein the surface of the PP substrate is activated after plasma pretreatment and sputtering of the adhesive layer, and the thickness of the PP substrate ranges from 2 to 50 μm.

3. The high-strength composite current collector with gradient CTE according to claim 1, wherein the thickness of the adhesive layer ranges from 5 to 10 nm.

4. The high-strength composite current collector with gradient CTE according to claim 1, wherein the total thickness of the gradient layer ranges from 20 to 50 nm; and the thickness of a single gradient layer is not less than 5 nm.

5. The high-strength composite current collector with gradient CTE according to claim 1, wherein the thickness of the buffer layer ranges from 20 to 50 nm.

6. The high-strength composite current collector with gradient CTE according to claim 1, wherein the thickness of the functional layer ranges from 200 to 1500 nm.

7. The high-strength composite current collector with gradient CTE according to claim 1, wherein the content of the adhesive layer component in the first gradient layer ranges from 70% to 99%, and the content of the functional layer component ranges from 1% to 30%; the content of the adhesive layer component in the second gradient layer ranges from 40% to 60%, and the content of the functional layer component ranges from 40% to 60%; the content of the adhesive layer component in the third gradient layer ranges from 1% to 30%, and the content of the functional layer component ranges from 70% to 99%. It comprises the following steps:

8. A method of making a high-strength composite current collector with a gradient CTE as claimed in any one of claims 1-7, characterized by, plasma activation of a PP substrate to obtain a pretreated PP substrate; sputtering on both sides of the pretreated PP substrate to prepare an adhesive layer; segmented double-target co-sputtering on the outer side of the adhesive layer to prepare a gradient layer; sputtering on the outer side of the gradient layer to prepare a buffer layer; sputtering on the outer side of the buffer layer to prepare a functional layer. It comprises a shell, a core and an electrolyte, and the core is formed by winding a positive electrode sheet, a separator and a negative electrode sheet, wherein the positive electrode sheet and the negative electrode sheet adopt the high-strength composite current collector with gradient CTE according to any one of claims 1-7.

9. A lithium-ion battery, characterized by ​

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