A cylindrical lithium-ion battery and a method of assembling the same

Abstract

This application relates to the field of lithium-ion battery technology, and more particularly to a cylindrical lithium-ion battery and its assembly method. The cylindrical lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a casing. The internal properties of the battery satisfy the following relationship: 0.95 ≤ R ≤ 1.10, where R = V. elec / (V elec + V res R is a dimensionless quantity, V elec V is the volume of the electrolyte. res The empty volume inside the casing after removing the positive electrode, negative electrode, and electrolyte is defined. This application characterizes the volume relationship between the electrolyte and the empty space inside the battery by defining a dimensionless parameter R, and controls R within a predetermined range. Simultaneously, it coordinates the positive and negative electrode thickness ratio to ensure that the cylindrical lithium-ion battery simultaneously meets the requirements of long cycle life and overcharge safety. This method guides battery design and is not dependent on specific battery dimensions or specific electrode material systems, thus possessing universality.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a cylindrical lithium-ion battery and its assembly method. Background Technology

[0002] Cylindrical batteries are widely used in consumer electronics, electric vehicles, and energy storage due to their mature manufacturing process, good consistency, and low cost. With the increasing adoption of larger cylindrical batteries such as the 4680, higher requirements are being placed on the cycle life and safety of cylindrical batteries.

[0003] Cylindrical batteries, especially cylindrical lithium-ion batteries, mainly consist of a positive electrode, a negative electrode, and an electrolyte. While the electrolyte does not provide capacity, its quantity significantly impacts the battery's performance. For example, insufficient electrolyte prevents adequate wetting of the battery electrodes, leading to increased lithium-ion transport impedance and rapid capacity decay during cycles. Simultaneously, loose electrodes result in severe localized lithium plating during overcharging, increasing the risk of thermal runaway. Conversely, excessive electrolyte can cause overcharging, leading to electrolyte decomposition and gas generation, causing a sudden increase in internal pressure. If the safety valve cannot adequately release pressure, this poses a fire and explosion risk.

[0004] Related technologies, such as Chinese patent CN118412634B, calculate the secondary electrolyte injection volume by considering the electrolyte consumption rate and battery life requirements during the formation process. This aims to address manufacturing issues such as extended electrolyte injection time in the workshop or insufficient electrolyte for formation. However, this approach primarily focuses on the electrolyte injection process itself and does not explore how to use the injection volume to guide battery structure design while ensuring the cycle life and overcharge safety of cylindrical batteries. Therefore, it is of guiding significance to move beyond solely focusing on the electrolyte injection process and instead establish a battery structure design method based on an electrolyte model. Summary of the Invention

[0005] This application provides a cylindrical lithium-ion battery and its assembly method. By defining a dimensionless parameter R to characterize the volume relationship between the electrolyte and the empty space inside the battery, and controlling R within a predetermined range, the cylindrical lithium-ion battery can simultaneously meet the requirements of long cycle life and overcharge safety by coordinating the thickness ratio of the positive and negative electrodes. This method can be used to guide battery design and is not dependent on specific battery sizes (18650 / 21700 / 4680) or specific electrode material systems, thus having universality.

[0006] To achieve the above objectives, this application adopts the following technical solution: The first aspect of this application provides a cylindrical lithium-ion battery, including a positive electrode, a negative electrode, an electrolyte, and a casing. The internal properties of the cylindrical lithium-ion battery satisfy the following relationship: 0.95 ≤ R ≤ 1.10, where R = V. elec / (V elec +Vres R is a dimensionless quantity, V elec V is the volume of the electrolyte. res The empty volume inside the housing after removing the positive electrode, negative electrode, and electrolyte.

[0007] In one possible implementation, 0.97 ≤ R ≤ 1.07.

[0008] In one possible implementation, the thickness of the positive electrode sheet is t. p With the thickness of the negative electrode sheet as t n , t p / t n The ratio ranges from 0.80 to 0.95.

[0009] In one possible implementation, t p The range is 100 ~ 120 μm.

[0010] In one possible implementation, t n The range is 115~135μm.

[0011] In one possible implementation, the housing is cylindrical, with a diameter ≥18mm and a height ≥65mm.

[0012] The second aspect of this application provides a method for assembling a cylindrical lithium-ion battery, comprising the following steps: S1. The positive electrode, negative electrode and separator are stacked and then wound into an electrode core; S2. Insert the electrode core into the housing; S3. Inject electrolyte into the casing, controlling the injection amount so that the internal properties of the cylindrical lithium-ion battery satisfy the following relationship: 0.95 ≤ R ≤ 1.10, where R = V elec / (V elec + V res R is a dimensionless quantity, V elec V is the volume of the electrolyte. res The empty volume inside the housing after removing the positive electrode, negative electrode, and electrolyte.

[0013] Furthermore, the range of R can be 0.97 to 1.07.

[0014] In one possible implementation, the amount of electrolyte injected is m elec The density ρ of the electrolyte satisfies the following relationship: m elec =ρ × R× (V cavity - V wound ), where V cavityV is the cavity volume of the shell. wound The compacted volume of the electrode core is given.

[0015] In one possible implementation, the density ρ of the electrolyte is in the range of 1.10~1.40 g / mL.

[0016] Compared with the prior art, this application has the following advantages: The first aspect of this application provides a cylindrical lithium-ion battery. First, by introducing a dimensionless quantity R and controlling R within a specific range, while simultaneously coordinating the positive and negative electrode thickness ratio, it is possible to simultaneously achieve a capacity retention rate of over 60% after 600 charge-discharge cycles and pass overcharge safety tests. Second, this parameter R has wide applicability, not dependent on specific battery sizes or electrode material systems, and is universally applicable to battery models such as 18650, 21700, or 4680. Third, the R parameter of this application can be directly used to guide battery design. After selecting the electrode thickness ratio, the target value of the residual space can be calculated based on the casing size to determine the required liquid injection volume. This method transforms the experience-driven liquid injection volume into a quantitative model-based design, effectively avoiding the tedious trial-and-error process in traditional R&D, significantly shortening the battery design cycle, and has guiding significance.

[0017] The second aspect of this application provides a method for assembling a cylindrical lithium-ion battery, which precisely matches the electrolyte injection amount according to specific parameter relationships satisfied inside the cylindrical lithium-ion battery, eliminating the need for trial and error while taking into account the battery's long cycle life and overcharge safety, thereby improving the battery's overall electrochemical performance. Detailed Implementation

[0018] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. It should be understood that the specific embodiments described are merely used to explain this application and are not intended to limit this application.

[0019] In the description of the embodiments of this application, it should be noted that all scopes disclosed in this application are to be understood to encompass any and all subscopes included therein. For example, the stated scope "100~120" should be considered to include any and all subscopes that begin with a minimum value of 100 or greater and end with a maximum value of 120 or less, such as 100 to 110, or 110 to 120, or 105 to 115. Furthermore, all scopes disclosed in this application are also considered to include the endpoints of the scope, unless otherwise expressly stated. For example, the scope "between 110 and 120" or "110 to 120" or "110-120" should generally be considered to include the endpoints 110 and 120.

[0020] This application introduces a dimensionless quantity R to characterize the volume relationship between the electrolyte and the available space inside a cylindrical lithium-ion battery. It defines the relationships between various factors and, by controlling R within a specific range while coordinating the positive and negative electrode thickness ratios, ensures that the cylindrical lithium-ion battery simultaneously meets the requirements for long cycle life and overcharge safety. Furthermore, the R parameter can directly guide battery design; after selecting the electrode thickness ratio, the target value of the remaining space can be calculated based on the casing dimensions, thus determining the required electrolyte injection volume. This reduces trial and error, improves R&D efficiency, and controls costs to some extent. In addition, the above design has broad applicability, is not dependent on specific battery sizes or electrode material systems, and is universally applicable to battery models such as 18650, 21700, or 4680.

[0021] To achieve the above objectives, this application adopts the following technical solution: The first aspect of this application provides a cylindrical lithium-ion battery, including a positive electrode, a negative electrode, an electrolyte, and a casing. The internal properties of the cylindrical lithium-ion battery satisfy the following relationship: 0.95 ≤ R ≤ 1.10, where R = V. elec / (V elec + V res R is a dimensionless quantity, V elec V is the volume of the electrolyte. res The empty volume inside the housing after removing the positive electrode, negative electrode, and electrolyte.

[0022] It's important to note that the physical significance of parameter R lies in identifying a critical window. When R is too small, there is insufficient electrolyte, resulting in substandard cycle life and overcharge safety. Conversely, when R is too large, there is excessive electrolyte, similarly deteriorating both cycle life and overcharge safety. Only within a suitable R range can both cycle life and overcharge safety be guaranteed to meet requirements simultaneously.

[0023] In some embodiments, R can be in the range of 0.97 to 1.07, for example, it can be any value or a range of any two values ​​among 0.97, 0.98, 0.99, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06 and 1.07.

[0024] In some embodiments, the thickness of the positive electrode sheet is t. p With the thickness of the negative electrode sheet as t n , t p / t n The ratio ranges from 0.80 to 0.95, and can be any value or a range of any two values ​​from 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.91, 0.92, 0.93, 0.94, and 0.95.

[0025] It should be noted that if t p / t n If the ratio of positive to negative electrode is too large, or the positive electrode is too thick or the negative electrode is too thin, it will lead to an imbalance in the capacity ratio of the positive and negative electrodes, an increase in interface impedance, and a loose internal structure of the electrode assembly. Consequently, both the cycle life and overcharge safety of the battery will fail to meet standards. Conversely, if t p / t n If the ratio is too small, the negative electrode sheet will be too thick relative to the positive electrode sheet, which will encroach on the effective space inside the casing, resulting in a decrease in the battery's volumetric and gravimetric energy density. Simultaneously, an excessively thick negative electrode sheet will increase the radial dimension of the winding core and the cyclic expansion stress, affecting the winding density and cycle life. Therefore, t p / t n The ratio of [specific component] to [specific component] must be controlled between 0.80 and 0.95 to ensure that both the battery's cycle life and overcharge safety performance meet the standards.

[0026] In some embodiments, t p The range is 100~120μm, for example, it can be 105~115μm.

[0027] If t p If the range is too large, it will increase the ion diffusion path and the radial dimension of the core, leading to increased rate polarization, poorer winding tightness, and reduced utilization of the internal space. Conversely, if t p If the range is too small, the positive electrode active material load per unit volume will be insufficient, resulting in low battery energy density and difficulty in matching the negative electrode capacity, causing the N / P ratio to run away and affecting cycle stability. Therefore, by using t pThe range is controlled within 100~120μm, which can be matched with the thickness of the negative electrode sheet, the compaction density and the internal space of the shell, taking into account both the transmission dynamics and the compactness of the core structure. This improves the volumetric energy density while reducing the risk of polarization and lithium plating, thus improving the rate performance and cycle life of the battery.

[0028] In some embodiments, t n The range is 115~135μm, for example, it can be 120~130μm.

[0029] If t n If the range is too large, it will encroach on the effective space inside the casing and increase the radial thickness of the core, leading to a decrease in the battery's volumetric energy density and amplified expansion stress during charging and discharging of the negative electrode, easily causing cyclic expansion and electrode cracking. Conversely, if t n If the range is too small, the active lithium may not be completely intercalated or deintercalated during charging, leading to lithium deposition on the negative electrode surface, posing a safety hazard and severely shortening cycle life. Therefore, the range of t... n The range is controlled between 115 and 135 μm, which is also matched with the thickness of the positive electrode sheet and the internal volume of the casing, taking into account the stability of the core structure and improving the cycle life and safety of the battery.

[0030] In some embodiments, the housing is cylindrical, with a diameter ≥18mm and a height ≥65mm.

[0031] Understandably, the outer diameter of the casing determines the final size series of the assembled cylindrical lithium-ion battery. For example, a cylindrical battery casing with an outer diameter of 21mm is used to manufacture 21-series cylindrical lithium batteries, such as the 21700 model battery. Cylindrical lithium-ion batteries satisfying this application can include 18650 model batteries with a diameter of 18mm and a height of 65mm, 21700 model batteries with a diameter of 21mm and a height of 70mm, and 4680 model large batteries with a diameter of 46mm and a height of 80mm. This indicates that the application scenarios of this application are not dependent on specific battery sizes and have universality.

[0032] Furthermore, this application may use a 4680 type cylindrical steel shell.

[0033] In some embodiments, the positive electrode sheet includes a positive current collector and a positive electrode material layer, the positive electrode material layer being disposed on at least one surface of the positive current collector. The positive electrode material layer includes a positive electrode active material, a conductive agent, and a binder. The positive electrode sheet can be prepared using methods conventional in the art.

[0034] The positive electrode active material is typically a conventional active material in the art, and may include LiNi. x Co y Mn z O2, LiFePO4 and LiMnx Fe y One or more of PO4, including LiNi x Co y Mn z In O2, x+y+z=1, 0.5≤x≤0.9.

[0035] Furthermore, the positive electrode active material can be selected from NCM811, NCM622, NCA, lithium iron phosphate (LFP), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523) and lithium manganese iron phosphate (LMFP) are any one or more of these.

[0036] The conductive agent can be selected from any one or more of graphite, carbon black, acetylene black, Ketjen black, and carbon nanotubes, and the binder can usually be selected from any one or more of polyvinylidene fluoride (PVDF), polyvinyl alcohol, and carboxymethyl cellulose.

[0037] The positive current collector is typically aluminum foil.

[0038] In some embodiments, the compaction density of the positive electrode material layer is 3.4 g / cm³. 3 .

[0039] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode material layer, wherein the negative electrode material layer is disposed on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode material, a conductive agent, and a binder. The negative electrode sheet may also be prepared using methods conventional in the art.

[0040] The negative electrode material may include graphite, silicon-carbon composite material (SiO2). x The conductive agent includes one or more of graphite, conductive carbon black, carbon nanotubes, acetylene black, and carbon fiber. The binder includes one or more of polyacrylic acid, styrene-butadiene rubber (SBR), polypropylene, starch, polyvinylpyrrolidone, carboxymethyl cellulose (CMC), and polyethylene.

[0041] In some embodiments, the negative electrode material layer may further include a thickener, such as sodium carboxymethyl cellulose.

[0042] The negative electrode current collector can be a conventional negative electrode current collector in the art, such as copper foil.

[0043] In some embodiments, the compaction density of the positive electrode material layer is 1.6 g / cm³. 3 .

[0044] In some embodiments, the electrolyte may be a conventional electrolyte used in batteries in the art, generally including non-aqueous solvents and lithium salts.

[0045] In some embodiments, the non-aqueous solvent may be a conventional non-aqueous solvent in the art, such as an ester solvent, and optionally any one or more of ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, ethylene sulfate, diethyl carbonate, and methyl propyl carbonate.

[0046] In some embodiments, the lithium salt may be a conventional lithium salt in the art, such as any one or more of LiPF6, LiBF4, LiClO4, and LiCF3SO3.

[0047] In some embodiments, 1.15M LiPF6 lithium salt is dissolved in a mixed solvent consisting of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 25:30:45, with an additional 1 wt% vinylene carbonate (VC) added as a film-forming additive.

[0048] In some embodiments, the density of the electrolyte can vary in the range of 1.10 to 1.40 g / mL, depending on the lithium salt concentration and solvent composition, for example, a density of 1.25 g / mL at 25°C.

[0049] In some embodiments, this application adopts a full-tab winding structure, with the positive and negative tabs welded to the current collector, without occupying any empty space inside the housing.

[0050] A second aspect of this application provides a method for assembling a cylindrical lithium-ion battery, comprising the following steps: S1. The positive electrode, negative electrode and separator are stacked and then wound into an electrode core; S2. Insert the electrode core into the housing; S3. Inject electrolyte into the casing, controlling the injection amount so that the internal properties of the cylindrical lithium-ion battery satisfy the following relationship: 0.95 ≤ R ≤ 1.10, where R = V elec / (V elec + V res R is a dimensionless quantity, V elec V is the volume of the electrolyte. res The empty volume inside the housing after removing the positive electrode, negative electrode, and electrolyte.

[0051] Furthermore, R can range from 0.97 to 1.07, for example, it can be any value or any two values ​​among 0.97, 0.98, 0.99, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06 and 1.07.

[0052] In some embodiments, the diaphragm may be a single-layer polyethylene (PE) diaphragm with a thickness of 12 μm and a porosity of 42%.

[0053] In some embodiments, the amount of electrolyte injected m elec The density ρ of the electrolyte satisfies the following relationship: m elec =ρ × R× (V cavity - V wound ), where V cavity V is the cavity volume of the shell. wound The compacted volume of the electrode core is given.

[0054] Among them, the cavity volume V of the shell cavity Calculated from the casing dimensions or measured using the water-filling method, for example, for a known battery model, where the height and diameter of the cylindrical casing are known, then V cavity =π× (d inner / 2)² × h inner .

[0055] The compaction volume V of the core wound The actual volume of liquid displaced after the electrode assembly is wound can usually be measured by the displacement method or the Archimedes method.

[0056] In some embodiments, the density ρ of the electrolyte ranges from 1.10 to 1.40 g / mL, and further, for example, can be 1.25 g / mL.

[0057] In some embodiments, the electrolyte volume V elec The injected electrolyte mass m can be calculated from the difference in cell mass before and after electrolyte injection. elec Then divide by the electrolyte density ρ to get: -V elec = m elec / ρ.

[0058] In some embodiments, the free volume V res =V cavity - V wound - V elec .

[0059] It is understandable that, according to the aforementioned calculation formula, the determination of the injection volume can be derived in reverse from the R parameter of this application, that is, after selecting the electrode thickness ratio, V is calculated based on the cavity volume of the shell and the compacted volume of the electrode assembly. elecThen, the injection volume can be determined by combining the electrolyte density.

[0060] The following examples will further illustrate this application.

[0061] All raw materials used in the embodiments of this application are commercially available.

[0062] Example 1 This embodiment 1 provides a cylindrical lithium-ion battery. A positive electrode and a negative electrode are laminated with a separator and wound to form an electrode core, which is then housed in a 4680-type casing. 5.2 g of electrolyte with a density of 1.25 g / ml is injected. The thickness t of the positive electrode is... p The thickness of the negative electrode sheet is 109 μm. n The electrode thickness is 128 μm, and the positive / negative electrode thickness ratio is 0.852. The electrolyte volume V was measured and calculated. elec = m elec / ρ = 4.16 mL, empty volume V res = V cavity - V wound - V elec The calculated value is 0.129 mL, at which point R = V elec / (V elec + V res = 0.970.

[0063] Cyclic performance testing results showed that the capacity retention rate after 600 cycles was 72%, exceeding the 60% standard. Overcharge safety testing results showed that the battery did not catch fire or explode under 1C / 10V overcharge conditions, thus passing the test.

[0064] Example 2 The only difference between Example 2 and Example 1 is that 5.4g of electrolyte was injected. The electrolyte volume V elec = 4.32mL, empty volume V res = -0.071 mL, R = V elec / (V elec + V res =1.017. All other conditions are the same as in Example 1.

[0065] Cyclic performance test results show that the capacity retention rate is 68% after 600 cycles. Overcharge safety test passed.

[0066] Example 3 The only difference between Example 3 and Example 1 is that 5.6g of electrolyte was injected. The electrolyte volume V elec = 4.48mL, empty volume V res= -0.271 mL, R = V elec / (V elec + V res =1.064. All other conditions are the same as in Example 1.

[0067] Cyclic performance test results show that the capacity retention rate is 63% after 600 cycles. Overcharge safety test passed.

[0068] Example 4 The only difference between Example 4 and Example 1 is that the thickness tp of the positive electrode is 112 μm, the thickness tn of the negative electrode is 125 μm, and the positive / negative electrode thickness ratio is 0.896. 5.6 g of electrolyte is injected, and the electrolyte volume V... elec = 4.48 mL, empty volume V res = -0.271 mL, R = V elec / (V elec + V res =1.064. All other conditions are the same as in Example 1.

[0069] Cyclic performance test results show that the capacity retention rate is 60% after 600 cycles. Overcharge safety test passed.

[0070] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that 5.0 g of electrolyte was injected. Electrolyte volume V elec = 4mL, empty volume V res =0.329 mL, R = V elec / (V elec + V res =0.924. All other conditions were the same as in Example 1.

[0071] Cyclic performance testing results showed that the capacity retention rate at 600 cycles was only 51%, lower than the minimum requirement of 60%. Overcharge safety testing was also failed.

[0072] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that 5.8g of electrolyte was injected. Electrolyte volume V elec =4.64 mL, empty volume V res = -0.471 mL, R = V elec / (V elec + V res =1.113. All other conditions are the same as in Example 1.

[0073] Cyclic performance testing results showed that the capacity retention rate was only 46% after 600 cycles. The overcharge safety test was also failed.

[0074] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that 6.0 g of electrolyte was injected. Electrolyte volume V elec = 4.8mL, empty volume V res = -0.673 mL, R = V elec / (V elec + V res =1.163. All other conditions are the same as in Example 1.

[0075] Cyclic performance testing results showed that the capacity retention rate was only 33% after 600 cycles. The overcharge safety test was also failed.

[0076] Comparative Example 4 The only difference between Comparative Example 4 and Example 2 is that the thickness tp of the positive electrode is 106 μm, the thickness tn of the negative electrode is 105 μm, and the positive / negative electrode thickness ratio is 1.01. All other conditions are the same as in Example 2.

[0077] The cycle performance test and the overcharge safety test both failed.

[0078] Comparative Example 5 The only difference between Comparative Example 4 and Example 2 is that the thickness tn of the negative electrode is 102 μm and the ratio of positive to negative electrode thickness is 1.07. All other conditions are the same as in Example 2.

[0079] The cycle performance test and the overcharge safety test both failed.

[0080] Effect Example Parameter definition and measurement method Electrolyte volume V elec The mass of electrolyte injected (m) is calculated by the difference in cell mass before and after electrolyte injection. elec Then divide by the electrolyte density ρ to get: -V elec = m elec / ρ.

[0081] The compaction volume V of the pole group wound The actual volume of liquid displaced after the electrode assembly is wound can be measured by the displacement method or the Archimedes method.

[0082] Shell cavity volume V cavity : Calculated from the shell dimensions (for a cylindrical shell of known height, V) cavity = π ×(d inner / 2)²× h inner (or measured by water injection).

[0083] Empty volume V resV res = V cavity - V wound - V elec Dimensionless parameter R: R = V elec / (V elec + V res ) The temperature conditions for the volume measurement mentioned above are the standard test temperature: 25 ℃, with an allowable deviation of ±1 ℃.

[0084] Performance testing methods Cyclic performance test At room temperature of 25°C, charge at a constant current of 1C to 4.25V, then charge at a constant voltage until the current drops to 0.05C; then discharge at a constant current of 1C to 2.75V. Repeat the above charge-discharge cycle 600 times, and record the percentage of the discharge capacity on the 600th cycle relative to the discharge capacity on the first cycle as the capacity retention rate.

[0085] Overcharge safety test According to the overcharge test method in GB / T 31485-2015 standard: the fully charged battery is charged to 10V at a constant current rate of 1C, and the battery is observed to see if it catches fire or explodes. The test pass standard is: the battery does not smoke, does not catch fire, and does not explode.

[0086] The parameters and effect data of Examples 1-4 and Comparative Examples 1-5 obtained are shown in Table 1: Table 1 Comparative Example 1 had a smaller R-value than Example 1, resulting in a lower capacity retention rate at 600 cycles than the minimum requirement, and it failed the overcharge safety test. Analysis suggests that a small R-value indicates insufficient electrolyte, inadequate electrode wetting, increased lithium-ion transport impedance, and accelerated cycle decay. Simultaneously, the presence of empty spaces within the electrode assembly leads to poor electrode contact, making localized lithium plating at the electrode / electrolyte interface more likely during overcharge, potentially causing thermal runaway. Comparative Examples 2 and 3 had larger R-values ​​than Example 1, similarly resulting in substandard cycle life and overcharge safety. Analysis suggests that a large R-value indicates excessive electrolyte; during overcharge, the electrolyte decomposes significantly, generating gas, causing a sudden increase in internal pressure, which the safety valve cannot adequately release, leading to thermal runaway.

[0087] Compared to Example 2, Comparative Example 4 mainly changed the thickness of the positive and negative electrode sheets. Analysis suggests that both the positive and negative electrode sheets were too thin, resulting in a smaller volume after compaction of the electrode assembly. This led to excessive residual space, insufficient inter-electrode pressure, high interfacial impedance, and a relatively insufficient electrolyte, causing both performance aspects to fail to meet standards. Comparative Example 5, compared to Example 2, mainly changed the thickness of the negative electrode. Analysis suggests that the thinner negative electrode sheet caused an imbalance in the positive / negative electrode capacity ratio (NP ratio), increased interfacial impedance, and a less compact internal structure of the electrode assembly, resulting in both performance aspects failing to meet standards. This indicates that when the electrode thickness ratio deviates from the preferred range, even electrolyte injection within the R window cannot achieve the desired performance, demonstrating a synergistic relationship between the electrode thickness ratio and the amount of electrolyte injected.

[0088] Although embodiments of this implementation have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this implementation, the scope of which is defined by the claims and their equivalents.

Claims

1. A cylindrical lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a casing, characterized in that, The cylindrical lithium-ion battery internally satisfies the following relationship: 0.95 ≤ R ≤ 1.10, where R = V elec / (V elec + V res R is a dimensionless quantity, V elec V is the volume of the electrolyte. res The empty volume inside the housing after removing the positive electrode, negative electrode, and electrolyte.

2. The cylindrical lithium-ion battery according to claim 1, characterized in that, 0.97≤R≤1.07。 3. The cylindrical lithium-ion battery according to claim 1, characterized in that, Let the thickness of the positive electrode sheet be t. p With the thickness of the negative electrode sheet as t n , t p / t n The ratio ranges from 0.80 to 0.

95.

4. The cylindrical lithium-ion battery according to claim 3, characterized in that, t p The range is 100 ~ 120 μm.

5. The cylindrical lithium-ion battery according to claim 3, characterized in that, t n The range is 115~135μm.

6. The cylindrical lithium-ion battery according to claim 1, characterized in that, The shell is cylindrical, with a diameter ≥18mm and a height ≥65mm.

7. A method for assembling a cylindrical lithium-ion battery, characterized in that, Includes the following steps: S1. The positive electrode, negative electrode and separator are stacked and then wound into an electrode core; S2. Insert the electrode core into the housing; S3. Inject electrolyte into the casing, controlling the injection amount so that the internal properties of the cylindrical lithium-ion battery satisfy the following relationship: 0.95 ≤ R ≤ 1.10, where R = V elec / (V elec + V res R is a dimensionless quantity, V elec V is the volume of the electrolyte. res The empty volume inside the housing after removing the positive electrode, negative electrode, and electrolyte.

8. The assembly method according to claim 7, characterized in that, 0.97≤R≤1.07。 9. The assembly method according to claim 8, characterized in that, The amount of electrolyte injected m elec The density ρ of the electrolyte satisfies the following relationship: m elec =ρ × R× (V cavity - V wound ), where V cavity V is the cavity volume of the shell. wound The compacted volume of the electrode core is given.

10. The assembly method according to claim 9, characterized in that, The density ρ of the electrolyte ranges from 1.10 to 1.40 g / mL.

Images