Electrode plate having active substance of electrochemical energy storage device

Abstract

This invention proposes an electrode sheet for an electrochemical energy storage device containing an active material, comprising a current collector and an electrode made of the active material located on the current collector. The active material comprises first particles in the form of spherical powder and second particles in the form of single crystal structure. The average particle size of the first particles is greater than or equal to three times the average particle size of the second particles. The volume ratio of the first particles in the active material is greater than the volume ratio of the second particles in the active material. Furthermore, the particle breakage rate of the electrode formed by the mixture of the first particles and the second particles is less than or equal to 40% during the rolling process.

Description

Electrochemical energy storage device electrode sheet with active material The present invention generally relates to an electrode sheet having an active material, and more particularly, to an electrode sheet having an active material formed from particles having two different particle size and volume ratios. Lithium-ion batteries are rechargeable batteries that convert chemical energy into electrical energy through the movement of lithium ions between the positive and negative electrodes. Due to their high energy density, good stability, and lack of memory effect, lithium-ion batteries are widely used in 3C products, power batteries, and energy storage batteries. To increase the energy density of lithium-ion batteries, active material particles are added to the battery electrodes. The density of the coating layer is increased by stacking the particles. Particles of a specific particle size are used to press the electrode sheets during the rolling process, further increasing the density of the electrode coating layer. However, in practice, factors such as the crystal structure, particle size, mixing ratio, and appearance of the particles can cause the particles to break during the rolling process, which in turn causes the electrolyte to penetrate the cracks in the particles and deteriorate the battery's cycle life. Therefore, technical personnel in this field need to further study and improve the active materials in lithium-ion battery electrodes in order to reduce the particle breakage rate of the active material particles during the rolling process. In view of the problems encountered in the aforementioned conventional technology, the present invention proposes an electrochemical energy storage device electrode sheet with an active material, which uses two particles with a specific particle size and volume ratio to form the active material. In this way, the particles in the active material will not be easily broken during the rolling process, and the optimal electrode density can be achieved. The present invention aims to provide an electrode sheet for an electrochemical energy storage device having an active material, comprising a current collector and an electrode composed of an active material disposed on the current collector. The active material comprises first particles in the form of a spherical powder and second particles in the form of a single crystal structure. The average particle size of the first particles is greater than or equal to three times the average particle size of the second particles. The volume ratio of the first particles in the active material is greater than the volume ratio of the second particles in the active material. Furthermore, the electrode composed of a mixture of the first and second particles exhibits a particle breakage rate of less than or equal to 40% during the rolling process. These and other objects of the present invention will become more readily apparent to the reader after reading the following detailed description of the preferred embodiment which is illustrated in various figures and drawings. The present invention will be described in detail below with reference to the accompanying illustrations, which form a part of the present invention and are presented in drawings and in a manner that illustrates specific embodiments in which the present invention may be practiced. These embodiments will be described in sufficient detail to enable a person of ordinary skill in the art to practice the present invention. For the sake of simplicity and convenience, the scale and proportions of certain parts in the illustrations may be deliberately reduced or exaggerated. Other embodiments or structural, logical, and electrical changes may be adopted in the invention without departing from the scope of the present invention. Therefore, the detailed description below should not be viewed in a limiting sense, and the scope of the present invention will be defined by the scope of the accompanying claims. A reader can generally understand a term, at least in part, from usage in context. For example, as used herein, the term "one or more" can be used to describe any feature, structure, or characteristic in a singular sense, or can be used to describe a combination of features, structures, or characteristics in a plural sense, depending at least in part on the context. Similarly, terms such as "a," "an," "the," or "said" can also be understood to convey singular usage or to convey plural usage, depending at least in part on the context. Additionally, the term "based on" can be understood to not necessarily be intended to convey an exclusive set of factors, but rather can allow for the presence of additional factors that are not necessarily explicitly described, again depending at least in part on the context. Readers can further understand that when words such as "include" and / or "contain" are used in this specification, they specify the existence of the stated features, regions, wholes, steps, operations, elements and / or parts, but do not exclude the possibility of the existence or addition of one or more other features, regions, wholes, steps, operations, elements, parts and / or their combinations. The following description of an embodiment of the present invention will now refer to FIG1 , which is a schematic diagram of a lithium-ion battery. It should be noted that while the present embodiment utilizes a lithium-ion battery structure as an example, the scope of the present invention is not limited to lithium-ion batteries. The principles and concepts of the present invention can be applied to any electrochemical energy storage device that utilizes an active material electrode sheet composed of a mixture of particles. Please refer to Figure 1. A lithium-ion battery 100 basically comprises a positive electrode sheet 110 (also called a cathode, which obtains electrons from an external circuit during discharge), a negative electrode sheet 120 (also called an anode, which releases electrons to an external circuit during discharge), an electrolyte 102, and a separator 104. In an embodiment, the positive electrode sheet 110 is composed of a current collector 112 and a positive electrode 114 located on the current collector 112, wherein the current collector 112 serves as a support for the active electrode material and also serves as a conductor between the electrode and the external circuit. The material of the current collector 112 can be a conductive metal, such as aluminum foil, with a thickness of approximately 1 to 25 μm. The positive electrode 114 mostly uses an intercalation compound as an active material to provide space for releasing and receiving conductive ions. The positive electrode 114 material of the present invention particularly uses an active material rich in lithium components, in which at least one transition element is mixed, such as a transition metal oxide complex, such as lithium nickel cobalt manganese oxide (LiNi x Co y Mn z O 2) or lithium nickel cobalt aluminum oxide (LiNi x Co y Al z O 2) where x+y+z=1, providing more intercalation space in the form of a layered structure. Regarding the negative electrode sheet 120, it can also be composed of a current collector 122 and a negative electrode 124 located on the current collector 122, wherein the material of the current collector 122 can be a conductive metal, such as copper foil, and the material of the negative electrode 124 can be carbon, such as graphite, graphene or carbon nanotubes, which has sufficient intercalation space to release and receive conductive ions and can prevent the accumulation of these conductive ions therein and cause the cycle life of the battery to deteriorate. As for other components, the electrolyte 102 inside the battery serves as a current channel in the form of conductive ions, which has better conductivity, smaller internal resistance, low melting point and high boiling point. The electrolyte 102 in the embodiment of the present invention can be composed of lithium salt and organic carbonate solvent, and the isolation membrane 104 is used to prevent contact short circuit between the positive electrode 114 and the negative electrode 124 and allow lithium ions to pass therethrough. In the embodiment, the material of the isolation membrane 104 can be polyolefin, such as polyethylene (PE) or polypropylene (PP). During the charging operation of the lithium-ion battery 100, lithium ions (Li +) will migrate from the lithium-rich positive electrode 114 and insert into the negative electrode 124 that can accept lithium ions. Each migrated lithium ion will release an electron (e - ), where lithium ions (Li + ) migrates through the electrolyte 102 through the separator 104 to the negative electrode 124, and the electrons (e - ) is directed from the positive electrode 110 through the external circuit 106 to the negative electrode 120. Conversely, the discharge operation of the lithium-ion battery 100 is essentially the opposite of the aforementioned charge operation. The higher the ratio of lithium ions returning to the positive electrode 114 during the discharge operation, the better the stability and cycle life of the lithium-ion battery 100. Please refer to Figure 2, which illustrates a positive electrode sheet 110 according to another embodiment of the present invention. In some embodiments, to increase battery energy density and space utilization, positive electrodes 114 may be formed on both sides of current collector 112. In the production of lithium-ion battery 100, the lithium-rich active material (such as LiNi x Co y Mn z O 2) It is usually first coated on the current collector 112 (on one side or both sides), and then pressed into the positive electrode 114 through a rolling process to increase its stacking density and reduce the thickness of the positive electrode sheet 110. The proportion of active material in the electrode can be greater than 80%, and the remaining proportion of the material can be a binder, such as polyvinylidene difluoride (PVDF), which can provide better electrochemical stability, wettability with the electrolyte 102, and suitable adhesion between the positive electrode 114 and the current collector 112. During the rolling process, the lithium-rich active material particles in the positive electrode 114 are compressed and densely packed. The thickness of the positive electrode 114 after rolling can be between 10 and 100 μm. The rolling process can easily cause the active particles to break, which in turn causes the electrolyte 102 to penetrate into the cracks of the active particles and deteriorate the battery cycle life. This is the problem that the present invention attempts to solve. Please refer to Figure 3, which schematically depicts two different particle stacking patterns in the positive electrode 114, based on different particle sizes. For active particles 114a and 114b of the same or similar particle size, as shown in the left half of the figure, some tightly packed particles 114b are inevitably crushed during the rolling process, resulting in a ductile stacking pattern, in which broken or deformed particles 114b are located between intact particles 114a. The greater the pressure applied during the rolling process, the higher the particle breakage rate. Active particle breakage can cause electrolyte to penetrate into particle cracks, seriously degrading the battery's cycle life. In contrast, as shown in the right half of Figure 3, active particles 114a and 114b with a large difference in particle size significantly avoid particle breakage. This is because during the rolling process, smaller particles 114b can easily and naturally stack to fill the spaces between larger particles 114a, resulting in a rigid stacking pattern with fewer broken or deformed particles. Please refer to Figure 4. This table lists several active particles #1~#4 used in the test, which are made of the same material (such as LiNi x Co y Mn z O 2), but differ in particle size, crystal structure, and appearance. The terms D10, D50, and D90 in the table are percentiles, which can be directly read from the statistical parameters of the particle size cumulative distribution function. They represent the particle size below the 10th, 50th, or 90th percentile of all particles, respectively. Generally speaking, as positive electrode active materials for lithium-ion batteries, larger particles offer greater mechanical strength to withstand compaction and prevent particle breakage, higher tap density to increase energy density, and smaller specific surface area (SSA) to prevent excessive interfacial side reactions. Smaller particles offer better packing properties, filling the spaces between larger particles during compaction and preventing particle breakage. The crystal structure of active particles can be either polycrystalline or single crystal. Generally speaking, single crystal particles have higher mechanical strength and fewer grain boundaries, offering better properties for avoiding particle breakage caused by compaction or frequent charge / discharge cycling. However, due to the cost of electrode materials, single crystal particles are significantly more expensive than polycrystalline ones. On the other hand, the shapes of the particles in the embodiments can be roughly divided into two types: spherical powders and irregular powders. Still referring to Figure 4. Four different particles #1 to #4 are used in the rolling test of the present invention to illustrate the relationship and results between the particle breakage rate and various particle properties, such as the aforementioned particle size, crystal structure, and appearance. These particles include particle #1, which is a polycrystalline spherical particle with a particle size D50 of approximately 13.6 μm. Particle #2 is a polycrystalline spherical particle with a particle size D50 of approximately 7.3 μm. Particle #3 is a single crystal irregular particle with a particle size D50 of approximately 3.5 μm. Particle #4 is a polycrystalline spherical particle with a particle size D50 of approximately 11.1 μm. As a single crystal particle, the porosity of particle #3 can be less than 1%. Please refer to Figure 5. This table lists the particle breakage rate and electrode density of the active material in the electrodes blended with particles #1-#4 for three test samples (including Control Group I, Control Group II, and the present invention). As can be seen from the table, Control Group I has the highest particle breakage rate of the three test samples. This is because its blended particles #1 and #2 are both polycrystalline, which have poor rolling resistance. The particle breakage rate referred to here is the ratio of broken particles among 100 randomly selected particles from a scanning electron microscope cross-sectional image of the electrode. Furthermore, due to the smaller average particle size of Control Group I (the larger particle size (75%) is the smaller particle #2, with an average particle size of only 7.3 μm), its electrode density is also lower. As for the control group II, as shown in the table in Figure 4, single crystal particles #3 were introduced into the electrode active material to be mixed with polycrystalline particles #1 and #2. This can be expected to improve the particle breakage rate of the control group II, which is lower than that of the control group I, which is a pure mixture of polycrystalline particles #1 and #2. However, the particle breakage rate is still higher than expected. This may be due to the fact that the larger, more mechanically strong particles #1 only account for a small volume ratio (20%) of the mixed powder. As shown in the table in Figure 4, the experimental group of the present invention uses a mixture of large polycrystalline particles (average particle size 11.1 μm) with a volume ratio of 70% and small single crystal particles (average particle size 3.5 μm) with a volume ratio of 30% to form the electrode active material. Compared with the two previous control groups, this formulation achieves a better particle size reduction rate (29%) and a higher electrode density (3.7 g / cm 3This is because the large, spherical particles #4, which make up a larger volume fraction of the powder mix, provide a higher stacking density. Furthermore, due to the high mechanical strength of the large particles, even in a polycrystalline form, they can withstand higher rolling forces. On the other hand, as shown in the right half of Figure 3, the small, spherical particles #3, which make up a smaller volume fraction of the powder mix, can fill the spaces between the large particles #4, providing higher structural strength for the entire powder stacking structure. It is important to note that the average particle size of the large particles #4 (11.1 μm) is greater than or equal to three times the average particle size of the small particles #3 (3.5 μm). This significant size difference avoids the ductile stacking pattern that causes particle breakage or deformation, as shown in the left half of Figure 3. Furthermore, the irregular shape of the small particles #3 also facilitates particle stacking and reduces the breakage rate. The single-crystalline structure of the small particles #3 increases their structural strength and reduces grain boundaries, thereby avoiding breakage issues caused by the rolling process and frequent charge / discharge cycles. Based on the above tests, the present invention proposes an electrochemical energy storage device electrode sheet having an active material, wherein the active material comprises first particles in the form of spherical powder and second particles in the form of single crystal structure, wherein the average particle size of the first particles is greater than or equal to three times the average particle size of the second particles, the volume ratio of the first particles in the active material is greater than the volume ratio of the second particles in the active material, and the particle breakage rate of the electrode composed of the first and second particles during the rolling process is less than or equal to 40%. The density of the electrode after the rolling process can be greater than 3.5 g / cm 3 , with a porosity of less than 25%. The average particle size of the first particles is approximately 11.1 μm, and the average particle size of the second particles is approximately 1-5 μm. The D50 of the first particles may be between 8-30 μm, and the D50 of the second particles may be between 1-5 μm. Those skilled in the art will readily appreciate that the apparatus and methods described herein are susceptible to numerous modifications and variations while maintaining the teachings of the present invention. Accordingly, the foregoing disclosure should be construed as limited only by the scope of the appended claims. 100: Lithium-ion battery 102: Electrolyte 104: Separator 106: External circuit 110: Positive electrode sheet 112: Current collector 114: Positive electrode 114a: Particles 114b: Particles 120: Negative electrode sheet 122: Current collector 124: Negative electrode This specification includes accompanying drawings, which form a part of this specification and are intended to provide a further understanding of the embodiments of the present invention. These drawings depict certain embodiments of the present invention and, together with the description herein, illustrate their principles. Among these drawings: FIG1 is a schematic diagram of a lithium-ion battery according to an embodiment of the present invention; FIG2 is a schematic diagram of an electrode sheet according to another embodiment of the present invention; FIG3 is a schematic diagram illustrating two different particle stacking patterns resulting from different particle sizes; FIG4 is a table listing particle data of different particle sizes, crystal structures, and shapes; and FIG5 is a table listing the particle breakage rate and density of active materials mixed with different particles in Control Group I, Control Group II, and examples. It should be noted that all figures in this specification are illustrative. For clarity and convenience, the size and proportions of the components shown in the figures may be exaggerated or reduced. Generally, the same reference symbols in the figures are used to indicate corresponding or similar features in modifications or different embodiments. 100:Lithium-ion battery 102: electrolyte 104: Isolation film 106: External circuit 110: Positive electrode 112: current collector 114: positive electrode 120: Negative electrode 122: collector 124: negative electrode

Claims

1. An electrode sheet for an electrochemical energy storage device containing an active material, comprising: a current collector; and an electrode comprising an active material located on the current collector, wherein the active material comprises first particles in the form of spherical powder and second particles in the form of single crystals; wherein the average particle size of the first particles is greater than or equal to three times the average particle size of the second particles, the volume ratio of the first particles in the active material is greater than the volume ratio of the second particles in the active material, the volume ratio of the first particles in the active material is 70%, the volume ratio of the second particles in the active material is 30%, and the particle breakage rate of the electrode composed of the first particles and the second particles during the rolling process is less than or equal to 40%, the particle breakage rate being the proportion of broken particles among one hundred particles randomly selected from a scanning electron microscope cross-sectional image of the electrode.

2. The electrode sheet of the electrochemical energy storage device having active material as described in claim 1, wherein the first particle is in the form of a polycrystalline spherical powder.

3. The electrode sheet of the electrochemical energy storage device having active material as described in claim 1, wherein the density of the electrode after the rolling process is greater than 3.5 g / cm3.

4. An electrode sheet for an electrochemical energy storage device having an active material as described in claim 1, wherein the porosity of the electrode is less than 25%.

5. The electrode sheet of the electrochemical energy storage device having active material as described in claim 1, wherein the average particle size of the first particles is 11.1 μm and the average particle size of the second particles is 3.5 μm.

6. An electrode sheet for an electrochemical energy storage device having an active material as described in claim 1, wherein the porosity of the second particles is less than 1%.

7. The electrode sheet of an electrochemical energy storage device having an active material as described in claim 1, wherein the first particles and the second particles contain at least one transition element.

8. The electrode sheet of the electrochemical energy storage device having an active material as described in claim 1, wherein the electrode further comprises a binder made of polyvinylidene fluoride (PVDF).

9. An electrode sheet for an electrochemical energy storage device having an active material as described in claim 1, wherein the thickness of the electrode is between 10 and 100 μm.

10. An electrode sheet for an electrochemical energy storage device having an active material as described in claim 1, wherein the electrode sheet is a negative electrode sheet and the material of the electrode is graphite, graphene or carbon nanotubes.

11. The electrode sheet of the electrochemical energy storage device having an active material as described in claim 1, wherein the material of the current collector is aluminum or copper, and the thickness of the current collector is between 1 and 25 μm.

12. The electrode sheet of the electrochemical energy storage device having active material as described in claim 1, wherein the D50 of the first particles is between 8 and 30 μm, and the D50 of the second particles is between 1 and 5 μm.

13. An electrode sheet of an electrochemical energy storage device having an active material as described in claim 1, wherein the electrode is formed on both sides of the current collector.

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