A pole piece and a battery

Abstract

The present invention provides a pole piece and a battery. The pole piece includes a current collector and an active material layer disposed on at least one side of the current collector. The active material layer includes active material particles, each of which includes a silicon-based material having a skeleton layer disposed thereon. The proportion of fluorine gradually increases from the silicon-based material toward the skeleton layer. The pole piece and battery provided by the present invention are designed to at least address the technical problem of battery volume expansion.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion batteries, and in particular to a pole piece and a battery. Background Art

[0002] Lithium-ion batteries are widely used in various fields. With the continuous development of electronic technology, higher requirements are placed on battery capacity and cycle performance. Research and development of negative electrodes with good electrochemical performance is a hot topic in lithium-ion battery research.

[0003] Most commercial lithium-ion batteries use graphite as their negative electrode, which has a specific capacity of only 372 mAh / g and is difficult to increase. Silicon, on the other hand, has a theoretical specific capacity of up to 4200 mAh / g and is widely available, inexpensive, and environmentally friendly. Electrodes made from silicon substrates can significantly increase the energy density of lithium-ion batteries. However, during the charge and discharge process, these electrodes expand in volume, causing the active material layer to pulverize and fall off, reducing the battery's cycling performance.

[0004] Therefore, there is an urgent need to solve the technical problem that the pole piece is prone to volume expansion. Summary of the Invention

[0005] The present invention provides a pole piece and a battery, which are used to at least solve the technical problem that the pole piece is prone to volume expansion.

[0006] In order to achieve the above-mentioned purpose, the present invention provides a pole piece, comprising: a current collector and an active material layer arranged on at least one side of the current collector, the active material layer comprising active material particles, the active material particles comprising a silicon-based material, the silicon-based material having a skeleton layer outside, and the proportion of fluorine element gradually increases from the silicon-based material to the skeleton layer.

[0007] The present invention provides a pole piece, which, because the silicon-based material is covered with a skeleton layer, can solve the problems of lithium insertion reaction after the pole piece is immersed in the electrolyte, silicon particle rupture, repeated growth-rupture-repair of the SEI film, large-scale accumulation of the SEI film during growth, battery expansion, lithium source consumption, capacity decay, low initial efficiency, and poor cycle life. The skeleton layer is rich in inert materials, which helps to improve the stability of the SEI film, thereby preventing volume expansion during the lithium insertion process of the pole piece and pulverization and shedding of the active material layer, thereby improving cycle performance and cycle life.

[0008] In one possible implementation, the proportion of carbon element gradually increases from the silicon-based material to the skeleton layer.

[0009] In one possible implementation, the proportion of silicon element gradually decreases from the silicon-based material to the skeleton layer.

[0010] In a possible implementation, the interface between the skeleton layer and the silicon-based material contains fluorine elements.

[0011] In one possible implementation, the active material particles further include a carbon-based material distributed around the skeleton layer.

[0012] In one possible implementation, phosphorus element is present at the interface between the skeleton layer and the carbon-based material.

[0013] In one possible implementation, sulfur elements are present at the interface between the skeleton layer and the carbon-based material.

[0014] In one possible implementation, the skeleton layer includes at least one of lithium fluoride or lithium carbonate.

[0015] In one possible implementation, the silicon-based material includes at least one of a silicon material and a silicon-oxygen material, wherein the mass of the silicon material and / or the silicon-oxygen material accounts for 7% to 50% of the mass of the active material particles; and / or

[0016] The carbon-based material includes at least one of graphite and hard carbon.

[0017] The present invention also provides a battery, comprising a sealed shell and a battery cell located inside the sealed shell, wherein the battery cell comprises a first pole piece and a second pole piece, and the second pole piece is the above-mentioned pole piece.

[0018] The electrode sheet and battery provided by the present invention enable the active material layer to come into contact with lithium ions in the lithium material layer in advance during the electrode sheet processing, thereby forming a skeleton layer. This process can reduce positive electrode lithium ion loss during formation, thereby increasing lithium ion utilization and improving the battery's initial efficiency.

[0019] In addition to the technical problems solved by the embodiments of the present invention described above, the technical features that constitute the technical solutions, and the beneficial effects brought about by the technical features of these technical solutions, other technical problems that can be solved by a pole piece and a battery provided by the embodiments of the present invention, other technical features included in the technical solutions, and the beneficial effects brought about by these technical features will be further described in detail in the specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0021] Figure 1 A schematic structural diagram of a pole piece provided in an embodiment of the present invention;

[0022] Figure 2 A point-scan SEM image of a pole piece provided in an embodiment of the present invention;

[0023] Figure 3 The pole piece provided in the embodiment of the present invention Figure 2 Line graph of element content changes at positions A, B, C, and D around the silicon material;

[0024] Figure 4 A comparison chart of the cycle performance curves of the battery provided by the embodiment of the present invention and the existing battery;

[0025] Figure 5 A comparison chart of the cycle performance expansion curves of the battery provided by an embodiment of the present invention and existing batteries.

[0026] Description of reference numerals:

[0027] 10-current collector;

[0028] 20-active material layer;

[0029] 30-Skeleton layer. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0031] Compared with graphite materials, silicon materials have the highest theoretical lithium insertion capacity of about 4200mAh / g, which can greatly improve the capacity of the battery. However, during the process of lithium insertion and removal, the silicon material electrode has a serious volume expansion effect, which can easily cause the active material layer to pulverize and fall off, reducing the battery capacity and cycle life.

[0032] After the electrode is immersed in the electrolyte, a lithium insertion reaction occurs, and the active material layer 20 contacts the lithium ions in the electrolyte to form a solid electrolyte interface (SEI film). During the battery charge and discharge cycle, silicon particles rupture, and the SEI film repeatedly grows-ruptures-repairs, causing a large amount of SEI film to accumulate during the growth process, resulting in battery expansion, consumption of lithium sources, capacity decay, low initial efficiency, and poor cycle performance.

[0033] In view of the above background, the electrode and battery provided by the present invention have an inorganic salt layer outside the core of the silicon material. The inorganic salt layer is rich in LiF inert substances, which helps to improve the stability of the SEI film, thereby avoiding the volume expansion of the electrode during the lithium insertion process and the pulverization and shedding of the active material layer, thereby achieving the effect of improving the cycle performance and cycle life.

[0034] The following describes a pole piece and a battery provided by the present application with reference to the accompanying drawings.

[0035] refer to Figure 1 As shown, the present invention provides a pole piece, comprising: a current collector 10 and an active material layer 20 arranged on at least one side of the current collector 10, the active material layer 20 comprises active material particles, the active material particles comprise a silicon-based material, and the silicon-based material has a skeleton layer 30 outside, and the proportion of fluorine element gradually increases from the silicon-based material to the skeleton layer 30.

[0036] Taking into account that when the electrode is immersed in the electrolyte and formed, a lithium insertion reaction will occur, silicon particles will rupture, the SEI film will repeatedly grow-rupture-repair, the battery will swell, the lithium source will be consumed, the capacity will decay, the first efficiency will be low, and the cycle will be poor, therefore, the present invention provides a electrode, which has a skeleton layer 30 on the outside of the silicon-based material. The skeleton layer 30 helps to improve the stability of the SEI film, thereby avoiding the volume expansion of the electrode during the lithium insertion process and the powdering and falling off of the active material layer 20, thereby achieving the effect of improving the cycle performance and cycle life.

[0037] In one possible implementation, the material of the skeleton layer 30 is an inorganic salt, and the skeleton layer 30 may be generated by inserting lithium in the lithium material layer into silicon particles in the active material layer 20 .

[0038] A lithium material layer may be provided on the surface of the active material layer 20 so that a skeleton layer 30 is formed outside the silicon-based material core. It is easy to understand that the lithium material layer is rich in metallic lithium, and the skeleton layer 30 is generated by a chemical reaction between lithium and the silicon-based material.

[0039] In one possible implementation, the skeleton layer 30 includes at least one of lithium fluoride (LiF) or lithium carbonate (Li 2 CO 3 ). Since the skeleton layer 30 is rich in LiF inert substances, the stability of the SEI film can be effectively improved.

[0040] The chemical reaction formula for generating the skeleton layer 30 is as follows:

[0041] PF6 - +ne - +nLi + →LiF↓+Li x PF y ↓

[0042] 2CO2+2e- +2Li + →Li2CO3↓+CO

[0043] By making the active material layer 20 contact with the lithium ions in the lithium material layer in advance during the processing of the electrode, the SEI film is formed in advance. When such an electrode is processed into a battery, the loss of positive electrode lithium ions can be reduced, thereby improving the utilization rate of lithium ions and achieving the effect of improving the initial efficiency of the battery.

[0044] In one possible implementation, the surface density of lithium in the lithium material layer is 0.09 mg / cm 2 to 0.5 mg / cm 2 , and the lithium material layer is disposed on the surface of the active material layer 20 by rolling.

[0045] In one possible implementation, the interface between the skeleton layer 30 and the silicon-based material contains fluorine elements, which can realize the formation of SEI film on the negative electrode sheet. Since the skeleton layer 30 is coated on the outside of the silicon-based material, the interface between the skeleton layer 30 and the silicon-based material is the first boundary position of the skeleton layer 30. Figure 2 At the position of point B in FIG, the first boundary position of the skeleton layer 30 is in contact with the silicon-based material.

[0046] In one possible implementation, the active material particles further include a carbon-based material distributed around the skeleton layer 30 .

[0047] In a possible implementation, the boundary between the skeleton layer 30 and the carbon-based material contains phosphorus. The boundary between the skeleton layer 30 and the carbon-based material is the second boundary of the skeleton layer 30, Figure 2 At point C in the diagram, the second boundary of the skeleton layer 30 contacts the carbon-based material. The second boundary of the skeleton layer 30 is opposite the first boundary of the skeleton layer 30. Phosphorus has high specific capacity and rate capability, which helps improve battery performance.

[0048] In a possible implementation, the boundary between the skeleton layer 30 and the carbon-based material contains sulfur element, and the boundary between the skeleton layer 30 and the carbon-based material is the second boundary position of the skeleton layer 30 .

[0049] In a possible implementation, the core is a silicon-based material; the active material particles further include a carbon-based material distributed around the skeleton layer 30 .

[0050] In one possible implementation, the silicon-based material includes at least one of silicon material and silicon oxide, and the mass of the silicon material and / or silicon oxide material accounts for 7% to 50% of the mass of the active material particles.

[0051] In one possible implementation, the carbon-based material includes at least one of graphite and hard carbon.

[0052] In one possible implementation, the silicon-based material includes a silicon-oxygen material, and the carbon-based material includes graphite. The graphite can be artificial graphite, natural graphite or modified graphite, wherein the mass of the silicon-based material accounts for 7% to 50% of the mass of the graphite, so that the amount of metallic lithium is adapted to the amount of the silicon-based material.

[0053] In one possible implementation, the silicon material includes silicon particles, the carbon-based material includes hard carbon material and graphite, and the graphite can be artificial graphite, natural graphite or modified graphite. Accordingly, the surface density of lithium in the lithium material layer is 0.09 mg / cm 2 ~0.5mg / cm 2 , so that the amount of lithium is compatible with the amount of silicon oxide material.

[0054] In one possible implementation, the silicon-based material includes a silicon-oxygen material, the carbon-based material includes a hard carbon material, and the surface density of lithium in the lithium material layer is 0.09 mg / cm 2 ~0.5mg / cm 2 , where the mass of silicon-oxygen material accounts for 7% to 50% of the mass of hard carbon material.

[0055] In one possible implementation, reference Figure 1 As shown, the electrode sheet provided by the present invention is a negative electrode sheet, and the current collector 10 can be made of copper foil, titanium foil, nickel mesh, stainless steel foil, lithium-copper alloy film or carbon cloth.

[0056] In a possible implementation, the active material layer 20 may be provided on one side of the current collector 10 , or may be provided on both sides of the current collector 10 .

[0057] In one possible implementation, the lithium material layer can be an ultra-thin metal lithium strip, which is prepared using asynchronous rolling technology. The lithium material layer is set on the surface of the active material layer 20 by rolling, so that the surface of the active material layer 20 is fully covered.

[0058] In order to construct an inorganic salt layer rich in LiF inert substances and prevent silicon from breaking into particles due to lithium insertion, which leads to repeated growth-rupture-repair of the SEI film, resulting in a large accumulation of SEI film during the growth process, battery expansion, consumption of lithium sources, capacity decay, low initial efficiency, and poor cycle performance, ultra-thin metal lithium strips are used for lithium replenishment, allowing the metal lithium to react with silicon to construct an inorganic salt layer of LiF inert substances around the silicon particles;

[0059] In one possible implementation, the proportion of carbon gradually increases from the silicon-based material to the skeleton layer 30. Figure 2 and Figure 3 As shown, from the silicon-based material to the skeleton layer 30, that is, along Figure 2 The direction indicated by the arrow is from point A to point D. Figure 3 As shown, the proportion of carbon elements at point A is 18%, the proportion of carbon elements at point B is 36%, the proportion of carbon elements at point C is 47%, and the proportion of carbon elements at point D is 61%. Obviously, the proportion of carbon elements gradually increases from the silicon-based material to the skeleton layer 30.

[0060] In a possible implementation, when the active material particles include graphite and silicon material, the proportion of carbon element gradually increases from the silicon-based material to the skeleton layer 30 .

[0061] In a possible implementation, the proportion of silicon gradually decreases from the silicon-based material to the skeleton layer 30. Figure 2 and Figure 3 As shown, from the silicon-based material to the skeleton layer 30, that is, along Figure 2 The direction indicated by the arrow is from point A to point D. Figure 3 As shown, the proportion of silicon elements at point A is 49%, the proportion of silicon elements at point B is 36%, the proportion of silicon elements at point C is 28%, and the proportion of silicon elements at point D is 18%. Obviously, the proportion of silicon elements gradually decreases from the silicon-based material to the skeleton layer 30.

[0062] It is easy to understand that when the active material particles include graphite and silicon materials, the proportion of silicon elements gradually decreases from the silicon-based material to the skeleton layer 30 .

[0063] In one possible implementation, the phosphorus content in the silicon-based material is 0.

[0064] Example 1

[0065] In this embodiment, the lithium material layer is metallic lithium foil, and the active material particles of the active material layer 20 include graphite and silicon oxide material. The mass of the silicon oxide material accounts for 7% of the total mass of the active material particles. Correspondingly, the surface density of metallic lithium in the lithium material layer can be 0.12.

[0066] Example 2

[0067] In this embodiment, the lithium material layer is metallic lithium foil, and the active material particles of the active material layer 20 include graphite and silicon oxide material. The mass of the silicon oxide material accounts for 20% of the total mass of the active material particles. Correspondingly, the surface density of metallic lithium in the lithium material layer can be 0.22.

[0068] Example 3

[0069] In this embodiment, the lithium material layer is metallic lithium foil, and the active material particles of the active material layer 20 include graphite and silicon oxide material. The mass of the silicon oxide material accounts for 30% of the total mass of the active material particles. Correspondingly, the surface density of metallic lithium in the lithium material layer can be 0.32.

[0070] Example 4

[0071] In this embodiment, the lithium material layer is metallic lithium foil, and the active material particles of the active material layer 20 include graphite and silicon oxide material. The mass of the silicon oxide material accounts for 40% of the total mass of the active material particles. Correspondingly, the surface density of metallic lithium in the lithium material layer can be 0.42.

[0072] Example 5

[0073] In this embodiment, the lithium material layer is metallic lithium foil, and the active material particles of the active material layer 20 include graphite and silicon oxide material. The mass of the silicon oxide material accounts for 50% of the total mass of the active material particles. Correspondingly, the surface density of metallic lithium in the lithium material layer can be 0.50.

[0074] In the above-mentioned embodiments 1 to 5, the lithium material layer is a metallic lithium foil, and the active material particles of the active material layer 20 include graphite and silicon oxide material, wherein the mass of the silicon oxide material accounts for 7% to 50% of the total mass of the active material particles. Accordingly, the surface density of lithium in the lithium material layer is 0.09 mg / cm 2 ~0.5mg / cm 2 This ensures that the amount of metallic lithium in the lithium material layer matches the amount of silicon particles. If the amount of metallic lithium is too large, lithium ions will react with the electrolyte and precipitate, reducing the utilization rate of lithium ions. If the amount of metallic lithium is too small, the lithium replenishment effect will not be obvious, and the improvement in the initial efficiency will not be obvious.

[0075] Example 6

[0076] In this embodiment, the lithium material layer is metallic lithium foil, and the active material particles of the active material layer 20 include hard carbon material and silicon oxide material. The mass of the silicon oxide material accounts for 7% of the total mass of the active material particles. Correspondingly, the surface density of metallic lithium in the lithium material layer can be 0.18.

[0077] Example 7

[0078] In this embodiment, the lithium material layer is metallic lithium foil, and the active material particles of the active material layer 20 include hard carbon material and silicon oxide material. The mass of the silicon oxide material accounts for 30% of the total mass of the active material particles. Correspondingly, the surface density of metallic lithium in the lithium material layer can be 0.28.

[0079] Example 8

[0080] In this embodiment, the lithium material layer is metallic lithium foil, and the active substances of the active material particles of the active material layer 20 include hard carbon material and silicon oxide material. The mass of the silicon oxide material accounts for 50% of the total mass of the active material particles. Correspondingly, the surface density of metallic lithium in the lithium material layer can be 0.34.

[0081] In the above embodiments 6 to 8, the lithium material layer is a metallic lithium foil, and the active material particles of the active material layer 20 include a hard carbon material and a silicon-oxygen material, wherein the mass of the silicon-oxygen material accounts for 7% to 50% of the total mass of the active material particles. Accordingly, the surface density of the metallic lithium in the lithium material layer is 0.09 mg / cm 2 ~0.5mg / cm 2 This ensures that the amount of metallic lithium is compatible with the amount of silicon, which not only avoids excessive metallic lithium causing metallic lithium to react with the electrolyte and precipitate, thereby reducing the utilization rate of lithium ions, but also avoids too little metallic lithium, which would result in insignificant lithium replenishment effects and insignificant initial efficiency improvements.

[0082] Here, a pole piece provided in an embodiment of the present application is selected. During processing, after the active material layer 20 is coated on the surface of the current collector 10, it is placed in a dry environment at a temperature of 90°C and baked for 24 hours to control the moisture content below 300 ppm to obtain a semi-finished pole piece. Then, asynchronous rolling technology is used to press the lithium ingot to the micron level to prepare an ultra-thin metal lithium strip, and the semi-finished pole piece is laminated to prepare a pole piece.

[0083] The present invention provides a battery, comprising a sealed shell and a battery core located inside the sealed shell, the battery core comprising a first pole piece and a second pole piece, and the second pole piece is the above-mentioned pole piece.

[0084] In a possible implementation, the first electrode is a positive electrode, and the second electrode uses the above-mentioned electrode as a negative electrode.

[0085] During processing, the first electrode piece, the second electrode piece and the isolation film are stacked in order so that the isolation film is located between the first electrode piece and the second electrode piece. The isolation film serves to isolate the first electrode piece and the second electrode piece. Then, the battery cell is wound to obtain a battery cell, which is placed in a sealed shell and an electrolyte is injected into the sealed shell. After vacuum packaging, standing, and formation, the battery cell is charged at a constant current of 0.1C to a state of charge (SOC) of 4%, and then charged at a constant current of 0.2C to a SOC of 10%, shaped, and capacity tested, a soft-pack lithium-ion battery is obtained.

[0086] In a possible implementation, the sealed housing may be an aluminum-plastic film, the electrolyte may be lithium hexafluorophosphate, and the isolation membrane may be an 8 μm coated diaphragm.

[0087] In order to illustrate that a pole piece provided by this application can improve the initial efficiency of the battery while improving the battery expansion effect through improvement, the following tests were conducted on the produced pole pieces:

[0088] Test 1: Cross-sectional morphology test

[0089] The electrode provided in this application was sputtered using a cross-section polisher (CP) to obtain a cross-section. The cross-section was then photographed using a scanning electron microscope (SEM) at a magnification of 500x-1.0kx. The white areas represent silicon particles, and it is clearly visible that the core of the silicon material is surrounded by a skeleton layer 30.

[0090] Test 2: Test the element content around the silicon material

[0091] The position of the SEM image was tested and analyzed using an X-ray energy dispersive spectrometer (EDS). Figure 2 Shown is a point-scan EDS image of a 5000x electron microscope image.

[0092] refer to Figure 2 The direction indicated by the arrow is from the silicon-based material to the skeleton layer 30, wherein position A is in the silicon-based material, position D is in the carbon-based material, and position B and position C are located between position A and position D. Position B is the boundary between the skeleton layer 30 and the silicon-based material, and position C is the boundary between the skeleton layer 30 and the carbon-based material. The elemental analysis references for positions A, B, C, and D are as follows: Figure 3 As shown. Figure 3 It can be clearly seen that from position A to position D, the proportion of carbon element gradually increases, the proportion of silicon element gradually decreases, and the proportion of fluorine element gradually increases and no longer changes to position C, that is, the proportion of fluorine element gradually increases and no longer changes to the junction position between the skeleton layer 30 and the carbon-based material. The content of phosphorus element in the silicon-based material is 0, the content of sulfur element in the silicon-based material is 0, and the content of fluorine element in the silicon-based material is 0.

[0093] The test results show that the proportion of C gradually increases and the proportion of Si gradually decreases from the silicon-based material to the skeleton layer 30. The element F begins to appear between positions A and C, indicating that the SEI film component LiF begins to form on the surface of the silicon particles between positions A and B. The structure of the skeleton layer 30 constructed on the surface of the silicon particles helps to improve the stability of the SEI film, thereby preventing volume expansion during the lithium insertion process of the electrode and the pulverization and shedding of the active material layer, thereby improving the battery's cycle performance and cycle life. At the same time, during battery formation, the lithium embedded in the second electrode can be released during the cycle to increase the battery capacity.

[0094] Test 3: Cyclic test and expansion test

[0095] The following cycling tests and expansion tests were performed on the batteries of the two comparison groups and the two experimental groups respectively. The only difference between the batteries selected by the two comparison groups and the batteries selected by the two experimental groups is that the batteries selected by the two experimental groups both use the electrode provided in this application as the second electrode, while the batteries selected by the comparison groups use a conventional second electrode and do not contain metallic lithium.

[0096] The testing process includes the following steps:

[0097] Step 1. Place the battery in a temperature environment of 5℃±2℃ for 10 minutes;

[0098] Step 2: Discharge the battery to the lower voltage limit at a battery discharge rate of 0.2C and let it stand for 10 minutes;

[0099] Step 3: Charge the battery at a charging rate of 0.7C to the upper limit voltage, cut off at 0.05C, and let it stand for 10 minutes;

[0100] Step 4: Discharge the battery at a rate of 0.2C to the lower voltage limit, and then perform an initial capacity test;

[0101] Step 5. Let the battery sit for 10 minutes.

[0102] Step 6: Charge the battery at a charging rate of 3C to the upper limit voltage, cut off at 0.05C, and then test the thickness of the battery;

[0103] Step 7. Leave the battery at a temperature of 25°C ± 2°C for 10 minutes.

[0104] Step 8: Discharge the battery at a 1C discharge rate to the lower voltage limit and let it stand for 10 minutes;

[0105] Step 9: Charge the battery at a charging rate of 3C to the upper limit voltage, cut off at 0.05C, and let it rest for 10 minutes;

[0106] Step 9: Repeat steps 8 and 9 1000 times, wherein in the 0-200 cycles, after every 50 cycles, the thickness of the battery is tested in the fully charged state; in the 200-1000 cycles, after every 100 cycles, the thickness of the battery is tested in the fully charged state; and in the temperature environment of 25°C, repeat steps 3 and 4 to perform capacity test; after 1000 cycles, the thickness of the battery is tested in the fully charged state.

[0107] Test 4: Capacity test

[0108] With batteries of the same target capacity and different lithium supplement surface densities, four experimental groups of batteries with different target capacities and one comparison group of batteries were processed. These batteries were placed in a constant temperature environment of 25°C, and charged to 4.48V at a battery charging rate of 1C with constant current and constant voltage, and then charged to 0.05C at a constant voltage cutoff. After standing for 5 minutes, they were discharged to 3V at a battery discharge rate of 0.2C, and the capacity data at 3V were compared.

[0109] The results are shown in Tables 1-4 below:

[0110] Table 1

[0111]

[0112] Table 2

[0113]

[0114] Table 3

[0115]

[0116] Table 4

[0117]

[0118]

[0119] It can be seen from Tables 1 to 4 that different silicon doping amounts, different target capacities, and different lithium supplement amounts are controlled. The 3V capacity of experimental groups 1 to 4 is significantly improved compared to that of comparison group 1. In batteries with different target capacities, the electrodes use metallic lithium with different surface densities, and the battery capacity is improved and reaches the target capacity value.

[0120] It can be intuitively seen from Tables 1 to 4 that the volume expansion rate of the batteries in the experimental group after 100 charge and discharge cycles is lower than the volume expansion rate of the corresponding control group batteries after 100 charge and discharge cycles, indicating that the present application can significantly improve the technical problem of the easy volume expansion of the electrode.

[0121] Refer to the test results of step 9 Figure 5 As shown, from Figure 5 As can be seen, the horizontal axis represents the number of charge and discharge cycles, and the vertical axis represents the expansion rate. The battery provided by this patent has a lower expansion rate when fully charged than existing batteries, significantly improving battery expansion. The battery provided by this patent, due to the formation of a silicate skeleton layer 30 in the second electrode sheet, can reduce relative expansion during cycling.

[0122] refer to Figure 4 The figure shows the cycle performance curve comparison of the battery provided by the present application and the existing battery. The horizontal axis represents the number of charge and discharge cycles, and the vertical axis represents the capacity retention rate of the battery. Figure 4 It can be seen that the battery provided by this patent has a capacity reduction of 80% after completing 450 charge and discharge cycles, while the existing battery has a capacity reduction of 80% after completing 350 charge and discharge cycles. Therefore, the battery provided by this patent has a battery cycle performance improvement of about 100 charge and discharge cycles, and the corresponding battery capacity retention rate is improved by about 5% to 15%. This shows that the improvement of this patent has a significant effect on improving the battery capacity and the battery cycle performance.

[0123] It should be noted here that the numerical values ​​and numerical ranges involved in this application are approximate values. Due to the influence of the manufacturing process, there may be a certain range of errors. Those skilled in the art may consider this part of the error to be negligible.

[0124] In the description of the present invention, it should be understood that the terms "center", "length", "width", "thickness", "top", "bottom", "up", "down", "left", "right", "front", "back", "vertical", "horizontal", "inside", "outside", "axial", "circumferential" and the like used to indicate orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the position or component referred to must have a specific orientation, a specific structure and operation, and therefore cannot be understood as limiting the present invention.

[0125] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0126] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connected," "fixed," etc. should be understood broadly. For example, they may refer to fixed or detachable connections, or integration; mechanical or electrical connections, or communication; direct or indirect connections through an intermediate medium, or internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0127] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A pole piece, characterized in that: include: A current collector (10) and an active material layer (20) disposed on at least one side of the current collector (10), wherein the active material layer (20) comprises active material particles, the active material particles comprise a silicon-based material, the silicon-based material has a skeleton layer (30) outside, the junction position between the skeleton layer (30) and the silicon-based material is a first boundary position of the skeleton layer (30), and the proportion of fluorine element gradually increases in a direction from the silicon-based material to the skeleton layer (30); The active material particles further include a carbon-based material distributed around the skeleton layer (30); the boundary position between the skeleton layer (30) and the carbon-based material is a second boundary position of the skeleton layer (30), and the second boundary of the skeleton layer (30) is opposite to the first boundary of the skeleton layer (30).

2. The pole piece according to claim 1, characterized in that: From the silicon-based material to the skeleton layer (30), the proportion of carbon element gradually increases.

3. The pole piece according to claim 2, characterized in that: From the silicon-based material to the skeleton layer (30), the proportion of silicon element gradually decreases.

4. The pole piece according to claim 3, characterized in that: The boundary between the skeleton layer (30) and the silicon-based material contains fluorine elements.

5. The pole piece according to claim 1, characterized in that: The boundary between the skeleton layer (30) and the carbon-based material contains phosphorus elements.

6. The pole piece according to claim 5, characterized in that: Sulfur elements are present at the interface between the skeleton layer (30) and the carbon-based material.

7. The pole piece according to any one of claims 1 to 4, characterized in that: The skeleton layer (30) includes at least one of lithium fluoride and lithium carbonate.

8. The pole piece according to claim 1, characterized in that: The silicon-based material includes at least one of a silicon material and a silicon-oxygen material, wherein the mass of the silicon material and / or the silicon-oxygen material accounts for 7% to 50% of the mass of the active material particles; and / or The carbon-based material includes at least one of graphite and hard carbon.

9. A battery, characterized in that: The invention comprises a sealed shell and a battery cell located inside the sealed shell, wherein the battery cell comprises a first pole piece and a second pole piece, and the second pole piece is the pole piece according to any one of claims 1 to 8.

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